Hip replacement navigation system and method

ABSTRACT

A hip joint navigation system is provided that includes a base having at least one channel disposed therethrough for receiving a pin for mounting the base to the pelvis. A mount feature is disposed on a top surface. A registration jig is configured to couple with the base and to engage anatomical landmarks. In some aspects, a patient specific jig system for hip replacement is provided including an engagement surface formed to closely mate to acetabular bone contours of a specific patient and a registration feature configured to be in a pre-determined orientation relative to an acetabulum the patient when the jig is coupled with acetabular bone contours of the specific patient. In other aspects, methods of using the systems are provided.

INCORPORATION BY REFERENCE TO ANY PRIORITY APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.16/437,546, filed Jun. 11, 2019, which is a continuation of U.S. patentapplication Ser. No. 14/643,864, filed Mar. 10, 2015, which claimspriority benefit to U.S. Provisional Patent Application No. 62/118,987filed Feb. 20, 2015 the entire contents of each is incorporated in itsentirety by reference herein. Any and all applications for which aforeign or domestic priority claim is identified in the Application DataSheet as filed with the present application are hereby incorporated byreference under 37 CFR 1.57.

BACKGROUND OF THE INVENTION Field of the Invention

This application is directed to the field of hip replacement, andparticularly to surgical tools and methods for guiding the preparationof the bones in connection therewith.

Description of the Related Art

Hip replacement surgery is common and getting more common by the year.One persistent issue with hip replacement is the relatively highincidence of poor placement of the cup and ball components of theprosthetic hip joint. For example, the cup is optimally placed in aspecific alignment with a plane including a rim of the acetabulum of thepelvis. For several reasons an unacceptably high percentage of patientshave the cup of the artificial hip joint out of alignment with thisplane.

Unfortunately, misalignment can lead to dislocation of the hip as soonas within one year of the implantation procedure. This is particularlyproblematic because recovery from a hip procedure can take many months.Patients undergoing a revision so soon after the initial implantationwill certainly be dissatisfied with their care, being subject toaddition redundant surgery. Of course, all surgery carries some degreeof risk. These poor outcomes are unsatisfactory for patients andsurgeons and are inefficient for the healthcare system as a whole.

Also, in cup placement in total hip arthroplasty, the inclination andanteversion angles are with respect to the Anterior Pelvic Plane(defined as a plane created by the two anterior superior iliac spines(ASIS) and the pubic symphysis). While these anatomical features arevisible/palpable while the patient is in a supine position, the majorityof total hip replacements are accomplished via a posterolateral approachwith the patient in some variation of a lateral position, in which mostof these landmarks are not accessible or visible. Historically,navigation for posterior approach hip replacement has been accomplishedby registering the anatomical features of the Anterior Pelvic Plane withthe patient first in a supine position and, once this plane is recordedby the navigation computer, moving the patient to a lateral position inorder to perform hip surgery—with navigation performed with respect tothe directly registered Anterior Pelvic Plane. This approach to hipnavigation is sub-optimal for surgical workflow because the extramovement of the patient from supine to lateral position takes moresurgeon and staff time and requires breaking sterility and re-draping.This is one of the key reasons why hip navigation has failed to beadopted by most of the market.

Additionally, altered leg length is a common patient complaint arisingfrom hip replacement surgery and has been a common cause of medicalmalpractice lawsuits that arise from hip replacement. Because part ofthe hip replacement procedure requires precise measurements of patientleg length and joint off-set that are frequently difficult to visualizeutilizing conventional instrumentation, there are opportunities toimprove the surgeon's performance of these measurements using computertechnology.

SUMMARY OF THE INVENTION

There is a need for improved systems and methods for providing forproper alignment of hip components with a patient's anatomy during a hipreplacement procedure. This can involve modular systems with low profilecomponents. This can involve a camera component designed to read alength measurement. This can involve techniques for measuring leg lengthand joint offset. This can involve techniques for locating one or morepoints on a fixed femur tracker.

In some embodiments, a hip joint navigation system is provided. The hipjoint navigation system can include a base comprising at least onechannel disposed therethrough for receiving a pin for mounting the baseto the pelvis and a mount feature disposed on a top surface. The hipjoint navigation system can include a registration jig configured tocouple with the base and to engage anatomical landmarks.

In some embodiments, the base has a lower surface configured to beplaced on the pelvis and where the at least one channel comprises twochannels for receiving threaded members to engage with the pelvis. Insome embodiments, the mount comprises a latch feature for removablysecuring a tower to the base. In some embodiments, the tower comprises alower end configured to secure to the mount and an upper end configuredto secure to an inertial sensor assembly. In some embodiments, the upperend is disposed at an angle (e.g., 35 degrees) to the lower end of thetower. In some embodiments, a mount feature is disposed between thelower end and the upper end of the tower, the mount feature configuredto be coupled with the registration jig. In some embodiments, theregistration jig includes an elongate member configured to be coupledwith the base, a housing having at least two degrees of freedom relativeto the elongate member, and a probe being slideably disposed through thehousing. In some embodiments, the probe comprises a distal portionangled relative to a proximal portion thereof. In some embodiments, theprobe is substantially straight along its length. In some embodiments,the probe includes a machine readable feature disposed on a side surfacethereof. In some embodiments, the machine readable feature comprises abinary code or other symbol. In some embodiments, the housing of theregistration jig includes a sensor mount configured to releasably attachto a sensor unit to position the sensor unit to read the readablefeature. The hip joint navigation system can include a sensor unitadapted to optically detect the machine readable feature on the probewhen coupled with the sensor mount.

In some embodiments, a femur jig is provided. The femur jig can includea base configured to securely couple with a proximal aspect of a femur.The femur jig can include a reference frame member configured to bedisposed above the base having a plurality of reference frame targets.In some embodiments, the base has at least one aperture therethroughconfigured to receive threaded pins to secure the base to the femur. Insome embodiments, the member is removably mountable to the base andcomprises an elongate upright member and an angled portion configures tobe oriented generally along the long axis of the femur. In someembodiments, the base is configured to be attached to the proximal femurwithin an incision prior to dislocation of the hip. In some embodiments,the reference frame member is accessible by a reference probe coupledwith the pelvis in use.

In some embodiments, a system includes the femur jig and a module forcomparing pre- and post-operative anatomical arrangement of the hipjoint is provided. In some embodiments, the module is adapted to comparepre- and post-operative anatomical arrangement of the hip joint usinganatomical landmark information derived from the acetabular rim. In someembodiments, the module is adapted include registration of a pluralitypoints on a rim of an acetabular shell implant to calculate the centerof rotation (COR) of the hip. In some embodiments, the module is adaptedto calculate at least one of a change in angle between the pelvis andfemur, a change in leg length, and joint offset. In some embodiments,the system displays an error message with guidance on re-positioning thefemur if a threshold value of joint angle, leg length or offset isexceeded. In some embodiments, the guidance advises the user toabduct/adduct, flex/extend, and/or internally rotate/externally rotatethe femur. In some embodiments, the base and reference frame member aredisposed on opposite sides of the same member. In some embodiments, thesame member comprises a thin plate structure. In some embodiments, themember is configured to conform to the femur to be low profile.

In some embodiments, a sensor unit for orthopedic navigation isprovided. The sensor unit can include a housing having an elongatestructure. The sensor unit can include an inertial sensor disposed atleast partially disposed within the housing. The sensor unit can includea camera at least partially disposed within the housing, the cameraoriented transverse to a longitudinal axis of the housing. In oneembodiment, the sensor unit has a transparent area on a side surfacethereof.

The sensor unit with a camera disposed in the housing can be combinedwith one or more other components in one or more systems. A system thatincludes the sensor unit can be coupled with a jig that includes acoupler that holds the sensor unit fixed relative to a device to beobserved by the camera. The sensor unit can be oriented with its widthor height extending along an extendable probe. The jig can include asliding bearing for allowing the probe to be moved along a range andwhile being moved to pass through a viewing area toward which the camerais directed. The probe can include a binary code or other symbol thatthe camera can read. In another system the sensor unit is coupled with auser interface device. The user interface device can be located insidethe surgical field in use. The user interface device can be coupled witha jig configured to mount to a bone, e.g., a pelvis, in use.

In some embodiments, a method of orthopedic navigation is provided. Themethod can include the step of detecting the orientation or positioningof a probe using inertial sensor. The method can include the step ofdetecting the extension of a probe using a camera. In some embodiments,the camera is positioned directly above the probe.

In some embodiments, a patient specific jig system for hip replacementis provided. The patient specific jig system can include an engagementsurface formed to closely mate to acetabular bone contours of a specificpatient. The patient specific jig system can include a registrationfeature configured to be in a pre-determined orientation relative to anacetabulum the patient when the jig is coupled with acetabular bonecontours of the specific patient.

The patient specific jig system can include an anatomical engagementportion. The patient specific jig system can include a registrationportion disposed laterally of the anatomical engagement portion suchthat the registration portion is disposed in a zone outside theacetabular rim. The patient specific jig system can include aregistration channel extending from an anterior surface of theregistration portion toward a posterior surface of the registrationportion.

The patient specific jig system can include a mount base configured tobe coupled with the pelvis adjacent to the acetabulum but spaced apartfrom a closest portion of the jig when the engagement surface is inengagement with acetabular bone contours. The patient specific jigsystem can include an inertial sensor device. In some embodiments, theregistration feature comprises a recess extending from an exposed faceof the jig. The patient specific jig system can include a channelextending posteriorly from an anterior side of the jig, the channelconfigured to receive a mounting pin of a navigation system. The patientspecific jig system can include at least two channels extendingposteriorly from an anterior side of the jig, the channel configured toreceive a mounting pin of a navigation system. In some embodiments, thechannels are disposed at an orientation related to a plane of theacetabulum.

In some embodiments, a patient specific method is provided. The methodcan include the step of coupling a patient specific jig to a rim of theacetabulum. The method can include the step of registering theorientation of a proxy for the plane of the acetabular rim using aninertial sensor device coupled with the patient specific jig. The methodcan include the step of removing the patient specific jig from theacetabulum. The method can include the step of orienting an acetabularshell in the acetabulum using an impactor and an inertial sensor device,wherein during orienting, inertial data from the inertial sensor deviceis used to confirm a proper orientation of the acetabular shell.

In some embodiments, the inertial sensor device is a first inertialsensing device and further comprising mounting a base on the pelvisadjacent to the acetabulum and coupling a second inertial sensing deviceto the base, the second inertial sensing device being fixed relative tothe pelvis. In some embodiments, the base is mounted at a location thatis independent of the patient specific jig. In some embodiments, thesecond inertial sensing device is configured to track motion of thepelvis and to generate an output that eliminates error due to themovement of the pelvis. In some embodiments, the second inertial sensingdevice includes a display providing a user interface. The method caninclude the step of coupling the first inertial sensing device with thebase to relate the orientation data of the first inertial sensing deviceto a reference frame of the second inertial sensing. In someembodiments, mounting the base comprises inserting at least a fixationpin through the patient specific jig along an axis disposed at apre-defined angle corresponding to the reference frame of the secondinertial sensing device. In some embodiments, mounting the basecomprises inserting at least two fixation pins through the patientspecific jig along an axis disposed at a pre-defined angle correspondingto the reference frame of the second inertial sensing device. In someembodiments, registering includes coupling the inertial sensor devicewith an impactor and coupling the impactor with the patient specificjig. In some embodiments, registering includes coupling a distal portionof the impactor with a registration feature of the jig at a specificpre-defined angular position. In some embodiments, registering includesaligning the inertial sensing device with an orientation symbol on thepatient specific jig prior to coupling the impactor with the patientspecific jig. The method can include the step of coupling the inertialsensor device with the impactor. The method can include the step ofchanging the orientation of the impactor in response to an outputreflecting the inertial data generated by the inertial sensing device.The method can include the step of aligning the acetabular shell to atarget anteversion angle. The method can include the step of aligningthe acetabular shell to a target inclination angle. The method caninclude the step of aligning the acetabular shell to a targetanteversion angle.

In some embodiments, a method of performing a hip joint replacementprocedure is provided. The method can include the step of placing apatient in a supine position, with a leg of the hip joint in an extendedposition. The method can include the step of mounting a laser projectingdevice to the pelvis adjacent to the hip joint. The method can includethe step of projecting a laser light onto the leg to illuminate aportion of the leg away from the hip joint. The method can include thestep of recording the position of incidence of the laser light. Themethod can include the step of registering a portion of the proximalfemur adjacent to the hip joint. The method can include the step ofreplacing the hip joint with an artificial hip joint. The method caninclude the step of projecting the laser light onto the leg and/or footto confirm orientation of the femur relative to the pelvis. The methodcan include the step of registering the portion of the proximal femuradjacent to the hip joint to confirm leg length and/or off-set.

The method can include the step of mounting an articulated member to thepelvis and coupling the laser projecting device to the articulatedmember. In some embodiments, the articulated member comprises a balljoint. The method can include the step of articulating the laserprojecting device to direct the laser light onto a portion of a foot ofthe leg. The method can include the step of locking the articulatingmember into a fixed configuration and maintaining the fixedconfiguration from at least step projecting a laser light onto the legto illuminate a portion of the leg away from the hip joint to stepprojecting the laser light onto the leg and/or foot to confirmorientation of the femur relative to the pelvis. In some embodiments,recording comprises marking three points on the surface of the leg andfoot coincident with the laser light. In some embodiments, recordingcomprises capturing a photographic image of the laser light and the legand/or foot. In some embodiments, registering the portion of theproximal femur comprises registering the femur at the greatertrochanter. In some embodiments, the step of projecting the laser lightonto the leg and/or foot to confirm orientation of the femur relative tothe pelvis includes recreating the recorded position by lining up theincidence of light with the leg and or foot. The method can include thestep of constraining the motion of the foot relative to the lower in legin at least one of step of recording the position of incidence of thelaser light and projecting the laser light onto the leg and/or foot toconfirm orientation of the femur relative to the pelvis. In someembodiments, the laser projecting device is disposed in a housingincluding an inertial measurement unit.

In some embodiments, a method of performing a hip joint replacementprocedure is provided. The method can include the step of mounting alaser projecting device to the pelvis adjacent to the hip joint. Themethod can include the step of registering a portion of the proximalfemur adjacent to the hip joint. The method can include the step ofprojecting laser light from the laser projecting device onto the legand/or foot to confirm correspondence between pre-operative orientationof the femur and pelvis and the post-operative orientation of the femurand pelvis. The method can include the step of registering the portionof the proximal femur adjacent to the hip joint to confirm leg lengthand/or off-set.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects and advantages are described belowwith reference to the drawings, which are intended to illustrate but notto limit the inventions. In the drawings, like reference charactersdenote corresponding features consistently throughout similarembodiments.

FIG. 1 is a perspective view of a hip navigation system applied to apatient illustrating a measurement of leg length and/or joint offsetafter implantation of the prosthetic hip joint.

FIG. 2 is an image of hip anatomy illustrating some examples ofanatomical landmarks that can be used in a method of navigating a hipprosthesis with the navigation system of FIG. 1.

FIG. 3 shows a navigation base assembly coupled with a first anatomicallandmark, in this case the ilium on the pelvis of the patient.

FIG. 4 is a perspective view illustrating first and second orientationdetecting devices coupled with the base of FIG. 3.

FIG. 5 is a perspective view of the navigating system, illustrating onetechnique for synchronizing a plurality of orientation and/or positiondetecting devices of the navigating system of FIG. 1.

FIG. 6 is a perspective view of the navigation system of FIG. 1 coupledwith the pelvis and illustrating a step of registering a landmark of afemur prior to resecting the femur.

FIG. 7 shows the anatomy after the femoral head has been resected and anoptional step of synchronizing a plurality of inertial sensors of thenavigation system.

FIG. 8 illustrates a step of registering an anatomical landmark disposedabout the acetabular rim on the pelvis.

FIG. 9 illustrates a step of registering another anatomical landmarkdisposed about the acetabular rim of the pelvis.

FIG. 10 illustrates initial placement of an impactor in the acetabulum.

FIG. 11 illustrates a hip prosthesis placement system, including aninertial sensing device.

FIGS. 11A-11C illustrate an embodiment of an impactor assembly.

FIG. 12 illustrates a step of navigating placement of a cup portion ofan artificial hip joint.

FIG. 13 is a perspective view of another embodiment of a hip navigationsystem.

FIG. 14 is a detail view of portion of the system of FIG. 13, with acamera recording linear position of a registration arm.

FIG. 15 shows a variation of the embodiment of FIGS. 13 and 14 in whichrotational orientation and linear position can be acquired by a cameraviewing a radial scale.

FIG. 16 is an exploded view of an assembly showing a tilt/rotationmechanism adapted to enable a camera to track at least one rotationalposition.

FIGS. 17-17C-2 illustrate modified systems configured for navigating aposterior approach hip replacement procedure.

FIG. 18 is a perspective view of a hip navigation system applied to apatient.

FIG. 19 is a perspective view of a fixation pin of the system of FIG.18.

FIG. 20A-20H illustrate various view of embodiments of a fixation baseof FIG. 18.

FIG. 21A-21G illustrate various view of embodiments of a first assemblyof FIG. 18.

FIG. 22A-22F illustrate various view of embodiments of a second assemblyof FIG. 18.

FIG. 23A-23C illustrate various view of embodiments of an orientationsensing device of FIG. 18.

FIG. 24A-24B illustrate various view of embodiments of a femur trackerof FIG. 18.

FIGS. 25A-25C are views of a hip navigation system applied to a patient.

FIG. 26A-26C illustrate various view of embodiments of a fixation baseof FIG. 25A.

FIG. 27A-28C illustrate various view of embodiments of a femur trackerof FIG. 25C.

FIG. 29 is a pre-operative x-ray.

FIG. 30 illustrates pre-operative positioning of a patient for aposterior approach technique.

FIG. 31 illustrates a configuration of the system of FIG. 18.

FIG. 32 illustrates anatomical landmarks registered during someembodiments.

FIG. 33 illustrates a first set of points on the rim of the shell.

FIGS. 34-38 illustrate a hip navigation system configured for anteriorapproach hip replacement procedures, and various aspects of suchprocedures.

FIG. 39 illustrates the positioning of the system of FIG. 18 in ananterior approach.

FIGS. 40-42 illustrate the positioning of another hip navigation systemin an anterior approach.

FIGS. 43-52 illustrate various aspects of methods involvingpatient-specific positioning jigs.

FIGS. 53-60 illustrate various aspects of methods involvingpatient-specific positioning jigs.

FIGS. 61A-63 illustrate various aspects of methods involvingpatient-specific positioning jigs.

FIG. 64 illustrates methods for defining a patient-specific safe zone ina hip placement procedure.

FIG. 65 is an embodiment of a system for close range optical tracking.

FIGS. 66-67 illustrate various anatomical landmarks that can be used invarious methods involving navigating with landmarks.

FIG. 68 is a pre-operative image that can be used to enhance alignmentin a hip procedure by providing patient specific data.

FIGS. 69 and 70 are views of a hip procedure navigation system appliedto a pelvis in a posterior approach.

FIGS. 71 and 72 are view of the hip procedure navigation system of FIG.69-70 modified and applied to a pelvis in an anterior approach.

FIGS. 73-73A illustrate a first embodiment of pin securement devices.

FIGS. 74-74B illustrate a second embodiment of pin securement devices.

FIGS. 75-75B illustrate a third embodiment of pin securement devices.

FIGS. 76-80 illustrate a modular system with an optical component.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A variety of systems and methods are discussed below that can be used toimprove outcomes for patients by increasing the likelihood of properplacement of a hip joint. These systems can be focused on inertialnavigation techniques, close range optical navigation, or a combinationof inertial and optical navigation.

I. Hip Navigation Using Inertial Sensors

Systems and methods described below can improve prosthetic hip jointplacement using navigation in connection with referencing anatomicallandmarks, incorporating preoperative custom fit jigs based on imaging,and a combination of pre-operative imaging and landmark referencing.These hip procedures generally guide a prosthetic hip to an orientationwithin the acetabulum that minimizes the chance of dislocation due toimpingement of the femoral neck on the cup or on bones around theacetabulum or other reasons related to suboptimal orientation of theprosthetic. Various techniques leverage population averages of properplacement while others are amenable to patient specific refinements.Also various techniques for registering and confirming the positionand/or orientation of the femur pre- and post-implantation are discussedherein, which are useful to control leg length and joint offset at theend of the procedure.

A. Navigation Using Inertial Sensors and Jigs for Referencing AnatomicalLandmarks with Posterior Approach

Most hip replacement procedures presently are performed from a posteriorapproach. In this approach, the patient is positioned on his/her sideand the anterior pelvic plane is oriented vertically, e.g.,perpendicular to the plane of the table on which the patient ispositioned. Most surgeons performing hip replacement are very familiarwith this approach and will immediately recognize the benefit ofenhanced certainty about the orientation of the relevant anatomy whenthe patient is in this position.

1. Posterior Approach: Systems with an Orientation Sensing DeviceCoupled to a Probe

FIGS. 1 and 4 show a hip navigation system 100 adapted to navigate a hipjoint procedure with reference to anatomical landmarks withoutrequiring, but not necessarily excluding, pre-operative imaging or otherinputs apart from those discussed below. The system 100 is shown mountedon a pelvis in a posterior approach in FIG. 1. FIG. 4 shows an earlyphase of a procedure prior to the joint being dislocated but after thesystem 10 is mounted to the pelvis. FIG. 1 shows a late phase of somevariations of techniques for which the system 100 is adapted. Asdiscussed further below, such variations involve registering the femurprior to and after the joint is replaced to confirm an aspect of therelative position and/or orientation of the femur, e.g., leg length,joint offset, and rotational orientation of the femoral neck.

The system 100 includes a registration jig 104, an alignment assembly108 and a landmark acquisition assembly 112. The alignment assembly 108is rigidly connected to the hip in the illustrated configuration so thatmotion of the hip cause corresponding motion of sensor(s) in theassembly 108 as discussed below. Sensing this motion enables the system100 to eliminate movement of the patient as a source of error in thenavigation. The landmark acquisition assembly 112 provides a full rangeof controlled motion and sensor(s) that are able to track the motion, inconcert with sensor(s) in the assembly 108. Additional details ofsystems, devices, sensors, and methods are set forth in U.S. Pat. No.8,118,815; US US2010/0076505; and U.S. Pat. No. 8,057,479 which are allincorporated by reference herein in their entireties for all purposes.The sensors in assemblies 108, 112 preferably transfer data amongthemselves and in some cases with external devices and monitorswirelessly, using Bluetooth, Wifi® or other standard wireless telemetryprotocol.

The registration jig 104 includes a fixation cannula 124 that has adistal end that can be advanced to a pelvic bone at an anatomicallocation or landmark or other selected location. In the illustratedtechnique, the cannula 124 is secured by a pin 132 (see FIG. 3) that isdriven into the ilium on the pelvis through the cannula 124. A distalend 128 of the pin 132 is shown in FIG. 1.

As discussed further below, the cannula 124 can be coupled with otherbones in other techniques with a posterior approach. For example, thecannula 124 can be coupled with the ischium or the pubis in othertechniques. In some techniques, the cannula 124 is mounted to a pelvicbone but not at a landmark. The hip navigation system 450 discussedbelow in connection with FIG. 17-17C-2 can be used such that thefixation member 466 is coupled at a point superior to the superior-mostpoint on the acetabular rim. In a specific technique, the member 466 isabout 10 mm above the superior-most point on the acetabular rim. In suchtechniques, three or more anatomical landmarks disposed about theacetabulum can be acquired, as discussed below. When the cannula 124 iscoupled with a landmark, only two additional landmarks are acquired insome embodiments as discussed below. In another variation, a clamp canbe used to couple with a bone without requiring that the pin 132 bedriven through the cannula 124 into the bone. For example, if the boneis thinner in the region where the system 100 is to be anchored, placingthe pin may be disadvantageous. FIG. 2 shows a region where a clamp maybe used beneath the point “A” on the ischium. One reason for mounting orclamping the cannula 124 away from the landmarks is that the landmarksmay not be visible or accessible before dislocating the hip joint. Ifthe clinician wishes to use the system 100 to reference the femur (asdiscussed below), it may be required to mount or clamp the cannula 124away from the landmarks.

FIG. 1 illustrates a step toward the end of a navigated hip jointimplant procedure discussed in detail below. Some of the preceding stepsinvolve removing the to-be-replaced joint, navigating the hip joint,preparing the implant location for the artificial joint, and placing thejoint, as elaborated below. As discussed further below, FIG. 1illustrates a technique for confirming that these steps were properlyperformed.

FIG. 2 shows some of the anatomy that is relevant to various methods andsystems herein. In some embodiments, the navigation system 100 isconfigured to locate a relevant anatomical feature to aid in properplacement of a prosthetic hip joint. For example, a plane can be locatedusing the system 100 that includes at least a portion of a patient'sacetabular rim. In practice, the acetabular rim may be uneven due todevelopment of ostephytes. So, in the context of this applicationlocating the anatomical plane can be an approximation of the actualtopography, for example an estimate of the plane, a plane including asubstantial fraction, e.g., a majority of the surface of the acetabularrim, or some other manner of estimating a relevant anatomical feature.Preferably the anatomical landmark being located is used to confirmaccurate placement of at least the cup and preferably the completeartificial hip joint.

FIG. 2 also shows an example of anatomical landmarks that can be used toapproximate the acetabular rim or another plane relevant anatomicallandmark. In many patients the acetabular rim is not well defined, dueto injury, advanced stages of arthritis or other conditions.Accordingly, approximating the acetabular rim for these patientsincludes calculating in the system 100 a plane that references but maynot include most or any of the actual acetabular rim. The plane that isdefined is located near the rim but more importantly has a knownanteversion and abduction angle relative to the anterior pelvic plane.For example, three points can be used to estimate the plane of theacetabular rim. In one technique, some or all of the points illustratedin FIG. 2 are used.

As illustrated by FIG. 2, three landmarks are defined at “A”, “B”, and“H”. The landmark “H” is located on the ilium at a location that isspaced away from the rim by an amount sufficient to avoid irregular bonygrowth due to injury, advanced stages of arthritis or other conditions,for example 1 cm superior to the most superior point on the acetabularrim. The landmarks “A” and “B” can be located on the ischium and pubisrespectively and can be similarly spaced from the rim to avoiddamaged/diseased areas. Each of these landmarks preferably is closeenough to the rim, however, to be within the standard open area, e.g.,the area exposed by the surgical cut down. Other landmarks that could beused include: anterior insertion point of trans-acetabular ligament tothe ischium, mid-point of the inferior aspect of the acetabular notch,the anterior superior iliac spine, anterior inferior iliac spine,convergence of the acetabulum and anterior inferior iliac spine, as wellas the other landmarks illustrate on FIGS. 66 and 67. In the techniquesdiscussed below all of the ilium, the pubis, and the ischium are used tolocate the acetabular rim. The navigation system 100 has one or moreprocessors that receive(s) data and determines the relative position ofthese (or other) anatomical landmarks from these points. The data can begenerated by inertial sensors, as discussed elsewhere herein, or othertypes of sensors. Preferably the sensors are small enough to be mountedon or in handheld housings or embedded in the instruments. Thenavigation system 100 preferably also has a memory device to at leasttemporarily store the position of these points or relevant orientationdata.

FIG. 3 shows further details of the registration jig 104 and furtheraspects of methods of navigating an artificial hip joint. A proximal endof the pin 132 is coupled with or disposed above a platform 136 that isconfigured to couple with the alignment assembly 108 and/or the landmarkacquisition assembly 112. As shown in FIG. 1, the platform 136 can beconnected to both of the alignment assembly 108 and the landmarkacquisition assembly 112 at the same time. The platform 136 comprises arigid bar fixed to the proximal end of the pin 132 and/or the cannula124 in the illustrated embodiment. The platform 136 includes a pluralityof mount features 140A, 140B, e.g., a mount feature on each of twolateral ends 144A, 144B of the platform. The mount feature 140A isconfigured to permit non-rotational attachment to the alignment assembly108.

FIG. 3 illustrates that the registration jig 104 is configured to beused in left and right hip procedures, for example having a dedicatedmount feature 140A for each hip. Preferably the mount feature 140Aprovides a post spaced away from the joint being treated so that thealignment assembly 108 can be mounted as far away from the hip joint aspossible. FIG. 5 shows the alignment assembly 108 on this post andanother post exposed. The exposed post is not used during the procedureon the hip joint illustrated in FIG. 5. However, if the other hip of thepatient is being treated, the platform 136 is in the oppositeorientation and the posted exposed in FIG. 5 will be coupled with thealignment assembly 108. Stated another way, a longitudinal axis of theplatform 136 extends between two mount posts, each of which can bededicated to a hip on one side of the medial-lateral mid-plane of thepatient.

The mount feature 140B enables rotational mounting of the landmarkacquisition assembly 112. For example, the mount feature 140B caninclude a pivotally mounted jig 148 that projects upward to a free endthat is adapted to mate with an orientation sensing device as discussedbelow. The joint 148 permits a registration arm, such as the elongatemember 224 discussed below to be tilted downward to touch landmarks atdifferent elevations.

In one technique, the registration jig 104 is preassembled and is driveninto a suitable anatomical landmark, such as the ilium. In othertechniques, an anchor jig can be mounted off-set from a landmark to beacquired. The ilium will have been previously identified by conventionalmeans, such as by X-ray examination, palpation, or by making an incisionand visually inspecting the pelvis. In one technique, the cannula 124,the pin 132, and the platform 136 are separable so that the pin can beplaced and the platform 136 coupled to the pin at a later time. Thecannula 124 can be coupled with other landmarks in some variations.

FIG. 4 illustrates further steps of various techniques. For example, thealignment assembly 108 can be coupled with the mount feature 140A. Inone embodiment, the alignment assembly 108 includes a rigid extension160 that is adapted to be mounted detachably to the mount feature 140A.The extension 160 has a first end 164 and a second end 168. The secondend 168 is detachably mountable to a surgical orientation device 172that detects orientation and rotation of the device 172 relative to areference frame. The orientation device 172 preferably comprises atleast one sourceless sensor, such as an accelerometer, a gyroscope, or acombination of these sensors and other sensors. In one preferredembodiment, the orientation device includes a three axis accelerometerto detect orientation relative to gravity and a plurality of gyroscopesto detect rotation. Other sensors could be used in variousmodifications. Examples of specific sensor combinations include AnalogDevices ADIS 16445 and Invensense MPU-6050 or MPU-9150 among others. Insome approaches, the orientation device 172 can be disposable and so thesensors preferably are less expensive sensors. Sensors on the landmarkacquisition assembly 112 may be reusable in some configurations and thusmay incorporate more expensive, more rugged or more accurate sensors.

The first end 164 of the detachable extension provides severalfunctions. The first end 164 has a device to engage the mount 140A in asecure but releasable manner. The engagement between the extension 160and the platform 136 minimizes or prevents relative movementtherebetween to avoid any mechanical relative movement during navigationprocedures so that movement of the orientation device 172 corresponds tomovement of the hip. The first end 164 also has a docking device that,as discussed further below, provides a stable and controlled manner toposition the landmark acquisition assembly 112 relative to theorientation device 172.

FIG. 4 also illustrates that the landmark acquisition assembly 112 canbe securely coupled to the platform 136, e.g., at the mount 140B. In oneembodiment, the landmark acquisition assembly 112 includes a gimbaledjig 200 and an orientation sensing device 204. The jig 200 includes acoupler 208 for detachably coupling with the mount feature 140B of theplatform 136. The coupler 208 is pivotally connected to a slidingsupport 212. The sliding support 212 includes a slot that permitsslideable extension of an elongate member 224. The slideable extensionpermits a range of motion of a distal end 228 of the elongate member tofacilitate acquiring a plurality of landmarks that are differentdistances from the attachment location of the cannula 124, as discussedfurther below. In other words, the distal end 228 can be extended awayfrom the axis of the sliding support 212 or can be retracted to aposition closer to the axis of the sliding support 212.

FIGS. 4 and 6 illustrate the movability of the landmark acquisitionassembly 112 relative to the platform 136 between two positions. In FIG.4, the elongate member 224 is swung about an axis that may be parallelto a longitudinal axis of the cannula 124 to move the distal end 228away from the first end 164 of the extension 160. This is a movingconfiguration of the gimbaled jig 200. In addition to rotation enabledby the pivotal coupling between the coupler 208 and sliding support 212,the pivotally mounted joint 148 can enable the elongate member 224 topivot about an axis that is not parallel to the axis of the cannula 124.The axis of rotation of the joint 148 can be perpendicular to the axisof rotation of the sliding support 212. This rotatability enables thedistal end 228 of the elongate member 224 to pivot down to contactanatomical landmarks, as discussed above. Additionally, the slidabilityof the elongate member 224 within the sliding support 212, discussedabove, enables the distal end 228 to move to reach anatomical landmarksin the same plane but closer to or farther from the distal end of thecannula 124 or pin 132. FIG. 6 shows the distal end 228 of the elongatemember 224 positioned closer to the platform 136 for referencinglandmarks at higher elevation or closer positions, e.g. on the lateralside of the femur.

FIG. 4 also shows that the distal end 228 can include an angled lengththat enables the elongate member 224 to avoid minor irregularities inheight adjacent to the anatomical landmarks being registered. Suchirregularities may be normal anatomy, osteophytes or irregular bonegrowth of various types.

FIG. 5 illustrates a parked configuration 260 of the landmarkacquisition assembly 112. In particular, a portion of the elongatemember 224 is moved into a latch 262 disposed at the first end 164 ofthe upright extension 160. The parked configuration 260 enables thenavigation system 100 to manage errors that can compound in someinertial sensors. For example, in one embodiment, gyroscopic sensors inthe orientation device 172 and in the orientation sensing device 204 canbe synchronized when a stable and known orientation is detected and oneor more of the gyroscopes, e.g., the gyroscope in the device 204, can bezeroed after that condition is met. Further techniques employing theparked configuration 260 will be discussed further below. As discussedbelow in connection with the system 450, some jigs have a registrationpoint adjacent to the distal end of the anchor jig or bone connectionsite. The system 450 is capable of accurately acquiring landmarks basedon only accelerometers operating in the device 204 in one mode. In sucha mode, a registration feature can provide an analogous function to theparked configuration, e.g., to enhance accuracy of the sensing devicesin the system.

Another example of a parked configuration of the system 100 can beprovided. For example, the parked configuration advantageously includesthe ability to stably position and hold the devices 172, 204 forsubstantially no relative movement. In one approach, the orientationsensing device 204 is mounted on the rigid extension 160. Otherarrangements could include a mounting post on the platform 136 adjacentto the rigid extension 160.

Where error management is less an issue, the parked configuration 260can still be useful in that it prevents unwanted swinging or othermovement in the surgical field.

In one basic method, the jigs discussed above are connected to thepelvic bone, the system 100 is put into the parked configuration 260,and the sensors are initialized. The initializing can includesynchronizing at least two sensors. In some cases, the initializing caninclude zeroing one or more sensors. In this context, “zeroing” is abroad term that includes any method of eliminating accumulated error inthe system, including any form of resetting of the sensors, and/orconfirming in one device that the data from the other device is reliablefor at least a fixed period.

FIG. 6 illustrates an optional step of acquiring a landmark of a femurin connection with a hip replacement procedure. The hip is positioned ina neutral flexion/abduction position. The landmark acquisition assembly112 is in a withdrawn configuration 266 with the elongate member 224moved, such as by sliding in the sliding support 212, to accommodate therelatively short distance from the platform 136 and a landmark of theproximal femur. In one technique the tip of the distal end 228 isbrought into contact with a part of the greater trochanter or elsewhereon the proximal femur. After the landmark is found and/or contacted, theclinician can make a mark Fm on the femur, such as a bovie mark, a penmark, a stitch or other durable indication. Once the tip of the distalend 228 is in contact with the desired landmark, the navigation system100 processes data from and stores the orientation of one or moresensor(s) in the orientation sensing device 204. Additionally, in someembodiments, the elongate member 224 is provided with a scale 226indicating position of the tip of the elongate member 224, e.g.,relative to the cannula 124 or some other relevant fixed feature of thepatient or the system 100. By providing the scale 226 to be read by theclinician, the system is made simple and cost effective.

After the optional step illustrated in FIG. 6, the proximal femur can beresected to remove the natural ball thereon.

FIG. 7 illustrates that in one advantageous technique, the user returnsthe system 100 to the parked configuration 260. This step may beoptional depending on the sensor(s) and the timing of the resecting ofthe femur. In this position, the sensor(s) in the orientation devices172, 204 can be initialized again, e.g., zeroed. As discussed above,this is one technique for minimizing accumulation of error in someinertial sensors. By providing this optional step, less costly sensorscan be used enabling the system 100 to deliver highly accurate hipreplacement while helping to manage cost for the patient, medicalprovider and healthcare system generally.

FIG. 8 illustrates a first extended configuration 264 provided in a stepafter the resecting of the proximal femur in which a second anatomicallandmark is acquired or referenced. In particular, the elongate member224 can be extended and can be rotated by the jigs 148, 200 to be incontact with any suitable landmark. In one technique, contact is madebetween the distal end 228 and the ischium. To provide maximum accuracy,this contact may be provided within a short period, e.g., within about20 seconds of being disengaged from the parked configuration 260. Oncecontact is made, the system 100 is configured to store the orientationof the sensing device 204. In one configuration, the orientation isstored after a button or other indirect means is pressed on theorientation device 172. In addition to acquiring the orientation, aposition value is input to the system. For example, the scale 226 on theelongate member 224 can be read by the user and the value of the scaleinput into the system. In one technique where the scale 226 is read andinput by the user, the orientation device 172 has a user interface withan input device for inputting such variables. As can be seen in thedrawings, the scale 226 can in fact be two different scales, one foreach of the retracted configuration 266 and the extended configuration264. Alternatively, the scale 226 can extend the entire length of theelongate member 224 to provide a greater range of positions that can beread by the clinician or by the system as in FIGS. 13 and 14.

The extended configuration 264 is one in which the distal end 228 of theelongate member 224 is adapted to touch an anatomical landmark locatedbetween the medial cephalad-caudal plane of the patient and theacetabulum of the pelvis.

Depending on the sensors used and the timing of landmark acquiring stepof FIG. 8, the user may return the system 100 to the parkedconfiguration 260 and also may initialize, e.g., zero, the system 100again.

FIG. 9 illustrates a second extended configuration 272 provided in astep after the resecting of the proximal femur in which a thirdanatomical landmark is acquired or referenced. The third anatomicallandmark can be acquired before the second anatomical landmark in sometechniques. In the second extended configuration the distal end 228 ofthe elongate member 224 moved to contact a landmark, such as the pubis.To provide maximum accuracy, this contact may be provided within a shortperiod, e.g., within about 20 seconds of being disengaged from theparked configuration 260. Once contact is made, the system 100 can storethe orientation of the sensing device 204. The orientation can be storedby pushing a button or other user interface device. In some techniquesorientation and position are input into the system. For example, thescale 226 on the elongate member 224 can be read by the user and thevalue of the scale input into the system. In one technique where thescale is read and input by the user, the orientation device 172 has aninput device, such as a user interface for inputting such variables.

The extended configuration 272 is one in which the distal end 228 of theelongate member 224 is adapted to touch an anatomical landmark locatedanteriorly of the acetabulum.

Once landmarks have been acquired, the system 100 can determine thebearing of three landmarks including that of the attachment location ofthe cannula 124, if the pin is attached to a relevant landmark. Thesystem can calculate the orientation of the orientation device 172relative the plane containing these three (or in other methods anothergroup of three or more) landmarks. From this, a variety of postprocessing can be performed. For example, the orientation (anteversionand/or abduction) can be adjusted based on the known mean orientation ofthe plane containing these three (or another three or more, if used)landmarks from the pelvic anatomic reference planes.

One variant of the system 100 enables a user to select between multiplesets of landmarks for use in the above calculations. The methoddiscussed above exploits the use of three points that are off of theacetabular rim. These points are less impacted by local prominences atthe rim that may be due to disease or deformity. Thus, they have a lowerlikelihood of requiring intra-operative improvisation. On the otherhand, another set of landmarks can be selected where the rim is free ofdeformities, which might be confirmed pre-operatively. For example, twoor three points can be selected on the acetabular rim for landmarkacquisition. The on-rim landmarks are advantageous in that they areeasier to access through a smaller incision. For example, on-rim pointscan include the center of the posterior insertion of the transacetabularligament, the center of the anterior insertion of the transacetabularligament and the most superior point on the rim. A group of anatomicallandmarks including one or more extra-acetabular landmarks can includethe ilium (where the registration jig 104 or other anchor member can beinserted), the lowest point of the acetabular sulcus of the ischium, andthe prominence of the superior pelvis ramus.

Some techniques involve referencing a fourth point. The fourth point canbe used in connection with some forms of patient specific registration.The fourth point can be extra-acetabular or can be disposed on theacetabular rim. An example of an acetabular landmark is the acetabularnotch. Other landmarks are discussed herein, for example in connectionwith FIGS. 34 and 35.

The posterior approach systems are advantageously configured to allowintra-operative selection between on-rim and off-rim points. Forexample, if the rim looks free of deformities pre-operatively but whenexposed presents differently, the surgeon can select an off-rim landmarkset.

Several techniques for enhancing the accuracy of the relationshipbetween the sensed landmarks and the location of calculated anatomicalfeatures, such as the anterior pelvic plane or angle of the acetabulumcan be employed. For example, user input can be collected indicatingwhether the hip being treated is on the left or the right side of thepatient and whether the patient is male or female. A more refinedestimation of the model can be provided based on a characterization of astudy group. For example, hip joints of a group of 30 or more patientscan be studied to identify the correspondence between a feature that canbe accessed in one approach and an anatomical feature of more surgicalrelevance that cannot. A group of subjects can be studied for any numberof demographic characteristics such as gender, age, weight, height orany other variable in a relevant population. For those sub-groups, acorrelation or transformation between a measured parameter and aparameter that cannot be measured but is desirable to know can begenerated. Once such a correlation or transformation is established,transforming a measured feature into the unmeasurable but useful to havefeature can be achieved by operating software on a processor. Thesoftware can be programmed to calculate one or two angles, e.g.,inclination and anteversion based on a registered pelvic plane, such asa proxy acetabular plane. Such a system can be used to generate in realtime the angles of a free hand instrument relative to the anatomy, e.g.,relative to an acetabulum in placing a hip socket component.

Additionally, data from the use of pre-operative imaging or positioning(discussed below) can be used to enhance the accuracy of thesecalculations. Thus, the posterior approach systems preferably areconfigured to take user input directly by actuating buttons on theorientation device 172 or by connecting an auxiliary data storagedevice, such as a flash memory device, to the system or by any means ofother communication with the system, including wifi connection,Bluetooth, Internet connection among others.

In some techniques, the posterior approach systems described herein areadapted to determine, monitor, and confirm proper leg length and jointoffset outcome in a hip replacement. For example, the system 100 cancalculate and store components of a leg length metric, e.g., a vectoralong the superior-inferior axis (leg length) and/or along themedial-lateral axis (offset). In one approach, the device 172 has adisplay that indicates when the femur is in the same position pre- andpost-operatively. For example, it can indicate “0” meaning nodisplacement causing a leg length change and “0” indicating no movementof the femur farther away from the cephalad-caudal mid-plane of thepatient pre- and post-operatively. For enhanced accuracy, a plurality ofpoints, e.g., three points, can be marked acquired and/or marked on thefemur. The points can be spaced apart by an amount sufficient to provideincreased accuracy. These three points can be used to confirm properplacement of the femur in abduction, rotation, and flexion.

One enhancement involves referencing the femoral neck to assure thatafter implanting the hip joint, the femur is positioned properlyrotationally. For example, it may be desired to make sure that a featureof the femur like the greater trochanter resides in the same rotationalorientation relative to an axis extending through the center of rotationof the femoral head and perpendicular to the plane of the acetabulum. Toassure a substantially unchanged rotation orientation post-implantation,the system 100 can record one or more, e.g., three points on the femoralneck pre- and post-implantation. Three points that would be convenientfrom either the posterior approach or the anterior approach (discussedbelow in connection with FIGS. 18-24B) are the greater trochanter,lesser trochanter and the insertion of the obdurator externus.

The foregoing are some steps that can be used to determine and store avariety of parameters useful in a navigated hip procedures. After someor all of these steps have been performed, in one embodiment, theacetabulum can be prepared for receiving a cup. For example, theacetabulum can be reamed in a conventional manner. In some embodiments,the reamer can be coupled with an orientation device containing aninertial sensor to guide the reaming process. This is discussed in somedetail in US2010/0076505, published Mar. 25, 2010 which is incorporatedby reference herein in its entirety for this purpose and for alldisclosure therein generally.

FIG. 10 shows that after reaming, an impactor 300 may be used to place acup of an artificial hip joint. The impactor handle 304 may bepositioned in the approximate correct orientation, e.g., with alongitudinal axis of the impactor being disposed perpendicular to theplane navigated above or a plane determined based on the navigatedplane. FIG. 10 shows that this initial placement can be done while thesystem 100 is in the park configuration 260. The impactor 300 can besubstantially aligned at this time, based on visual inspection. As partof the step illustrated in FIG. 10 or shortly thereafter, the sensorscan be initialized, e.g., zeroed as discussed above.

FIG. 11 shows that in a subsequent step the orientation sensing device204 can be undocked from the proximal end 230 of the elongate member 224and thereafter docked to the impactor 300. Preferably this step isperformed while the impactor 300 is in place on the hip, close theproper alignment. In another embodiment, a third sensing device similarto the sensing device 204 be coupled with, e.g., pre-attached to, theimpactor and the data collected above transferred to the third device.The impactor 300 and sensing device 204 comprise a cup orientationnavigation assembly. Preferably the impactor 300 has a cylindrical shell312 that is moveable relative to an inner shaft 316 of the handle 304.The shell has a docking device 320 that can receive the docking deviceof the sending device 204. The movability of the shell 312 helps toisolate the sensing device 204 from the forces that are transmittedthrough the impactor 300. These forces are applied by a mallet or otherdevice for forcibly moving the cup into position. By providing at leastsome force isolation between the shell 312 and the sensing device,impact on the sensors in the sensing device 204 can be reduced.Excessive force being applied to the sensing device 204 can put thedevice 204 out of service, for example until synched with the device172.

FIG. 11A illustrates a further embodiment of an impactor 300A in whichthe movement of a shell 312A is cushioned by a plurality of springmembers 340, 344 which are configured to absorb at lease some of theshock of the impact on the impactor 300A. The impactor 300A also isconfigured to be modified to suit any of a plurality of hip prostheses.For example, a plurality of tip components 348 can be provided in a kitwhere each tip component is attachable to and detachable from a distalend of the shaft 316A of the impactor 300A.

FIGS. 11B-C show more detail of distal features of the impactor 300A. Inparticular, the tip component 348 is removable from a shaft 316A of theimpactor 300A. FIG. 11C shows that the tip component 348 can have arecess 352 formed on the proximal side thereof and an engagement device356 formed on the distal side thereof. The recess 352 can comprises aplurality of flats 350A corresponding to a plurality of flats 350B onthe distal end of the shaft 316A. The flats permit proximal-distalsliding of the recess 352 over the distal end of the shaft 316A.Preferably a detent device or other mechanism is provided between thetip component 348 and the shaft 316A so that the component does not falloff the shaft. The flats prevent the tip components 348 from rotatingrelative to the shaft 316A. The engagement device 356 comprises threadsin one embodiment so that the cup 360 of the prosthetic hip can bescrewed onto the distal end of the tip component 348. The slidingengagement of the tip component 348 on the shaft 316A is importantbecause the impactor 300A is intended to be used with hip prostheses ofa variety of manufacturers. Often the cup 360 will have a hole patternfor securing the cup to the prepared acetabulum that is unique to themanufacturer and that is dictated by the anatomy. The flats enable manydiscrete alternate relative angular positions of the tip component 348(and hence the cup 360) to the shaft 316A. A plurality of flutes orelongate axial ridges 364 on the outer surface of the tip component 348enable the user to securely grasp the tip component for mounting anddismounting the tip component on the shaft 316A.

FIG. 12 shows the cup orientation placement navigation assembly of FIGS.11A-C adjacent to the anatomy. This figure also illustrates a free-handnavigation configuration 274, in which at least the orientation devices172, 204 are capable of six degrees of motion relative to each other.Any of the variations of FIG. 11A-11C could be substituted in theillustration. In particular, the handle 304 is oriented as desired. Inone embodiment, the system 100 displays in real time the angle of thecup relative to the navigated plane, which was acquired as discussedabove. Angles that can be displayed include any one or more ofanteversion and abduction for example. Preferably the clinician canconfirm the position of the cup within a short fixed time, such aswithin about 20 seconds. In one embodiment, the angles displayed can beadjusted by about 40 degrees abduction and 20 degrees anteversion. Theseangles are not critical, but they relate to the range of motion of theleg. It is preferred to be close to these angles because motion inabduction and anteversion extends on either side of these angles. It isbelieved that the systems discussed herein can increase the percentageof patients in a “safe zone” close to these angles, typically describedas within 10 degrees of these angles. In contrast, studies show thatconventional techniques yield close to 50% of patients outside the “safezone.”

Depending on the sensors and the timing of cup placement step of FIG.12, the user may mount the sensing device 204 on the elongate member 224again and may return the system 100 to the parked configuration 260 andalso may initialize or zero the system 100.

The system 100 can be configured to provide a pre- and/or post-operativeestimation of an angle relative to the angle of the table. In theposterior approach, the patient is placed on his/her side. In thisapproach, there is more chance for the patient's position to shiftintra-operatively. In one embodiment, an alignment rod can be coupledwith the sensing device 204 and aligned with the plane of the table. Theorientation of the sensing device 204 when so aligned is recorded in thesystem. Later in the procedure, one or more angles is calculated anddisplayed to the user based on the assumption that the pelvis has notmoved. At such later stages, the orientation of the sensing device 204can be confirmed again relative to the table to provide informationabout whether the patient has moved. If significant movement hasoccurred, such that any assumptions of no movement are violated, some orall of the landmark acquisition steps can be repeated. Alternatively,the movement of the pelvis can be tracked by the sensing device andcorrected for. The manner of incorporating the table orientation withlandmark acquisition is discussed in greater detail below.

The user will have placed the artificial ball of the replacement hipjoin in the proximal femur and thereafter can place the ball in the cup,which was properly oriented using the techniques discussed above.

FIG. 1 shows that thereafter, the user can optionally confirmorientation and/or leg length using the system 100. The leg with theartificial hip joint assembled is placed in a neutral flexion and/orabduction and/or rotation position. The acquisition assembly 112 can beplaced in the retracted configuration 266. The distal end 228 of theelongate member 224 can be brought into contact with a landmark, whichmay be the same landmark acquired in FIG. 6. Once contact is made withthis landmark (e.g., the bovie mark), the orientation of the sensingdevice 204 is determined by the system 100. Also, the distance indicatedon the scale 226 of the elongate member 224 is input into the system inany of the manners discussed above (e.g., manual or sensed). The system100 can thereafter calculate components of vectors along the S-I axis(leg length) or M-L axis (offset).

Once leg length and offset are determined post-operatively, they can becompared the pre-operative measurements (FIG. 6) to let the surgeon knowif any adjustments should be made before completing the hip replacementsurgery.

FIGS. 13 and 14 show other embodiments of a hip navigation system 400that can include any of the features discussed above. In addition, thesystem 400 includes a free-hand sensor mount 404 that can be used tomount a freehand orientation device 204A in one configuration. Thefreehand orientation device 204A preferably includes inertial sensors,similar to those hereinbefore described. The device 204A preferably alsoincludes a camera 412. The field of view is illustrated by the coneprojecting downwardly from the base of the freehand orientation device204A. FIG. 14 shows that the field of view includes a window 418 in asliding support 420. The window 418 enables the scale 226 to be viewedtherethrough.

Because hip replacement procedures involve an open surgical field with asubstantial amount of exposed tissue and blood the line of sight thecamera 412 to the scales can become obstructed. In one embodiment, ahood is provided above the window 418. The hood keeps most of the bloodand tissue out of the space where the camera views the scales.Additionally, a scrubber component, e.g., a thin rubber member, can beprovided above the scales 226, 226A (discussed below) to prevent thistissue or fluids from entering into the field of view laterally.

One advantage of the system 400 is that the camera 412 can automaticallyprocess the image captured through the window 418 and thereby determinethe position of the elongate member 224 relative to the sliding support420. A further advantage of this is to eliminate one step from thenavigation process, e.g., to eliminate the need to enter the lineardimension into the system 400. Eliminating the step can reduce timeand/or personnel in the operating room. Also, the camera 412 can beconfigured to read a much higher resolution than can be read by aclinician. This can provide greater accuracy in the system overall. Notonly that, but the camera can be configured to make fewer or no errorsin reading the position, which can improve outcomes overall. Forexample, miniature cameras can produce data in JPEG or other imageformat that a processor in one or both the orientation devices 172, 204Acan process to extract the linear position of the elongate member 224.

A further modified embodiment is described in FIG. 15, which shows anarcuate scale 226A that can be positioned on a structure beneath theelongate member 224, e.g., on a structure beneath the orientation device204A that is rotationally fixed relative to an axis extending out of thepage. FIG. 16 shows one configuration with this arrangement. A pivot 440enables the sliding support 420 to rotate about an axis extending upwardon the page. Although the pivot 440 is fixed about this upward extendingaxis, it can rotate about a pivot 444. A window 418A in the elongatemember 224 enables the camera to see through the support to view thescale 226A disposed on an arcuate or disk shaped feature of the pivot440. The scale 226A can be read by the camera 412 or a second camera toprovide accurate determination of the rotational position of theelongate member 224. This can enable one of the sensors in theorientation device 204A to be eliminated or inactivated. In anotherembodiment, camera date derived from the scale 226A can be used toconfirm the data from sensors in the orientation device 204A. Preferablythe scale 226A has markings over a range of from about 15 to about 90degrees, for example, between about 30 and about 60 degrees, e.g., atleast between about 40 and about 50 degrees.

2. Posterior Approach: Systems Adapted for Accelerometer Sensitivity

FIGS. 17-17C2 illustrate further embodiments. A system 450 is adaptedfor navigating a hip procedure from a posterior approach. The system 450includes an anchor jig 454, an alignment system 458, and a landmarkacquisition assembly 462. The components may be similar in some respectsto those discussed above, and such descriptions are incorporated withthis embodiment where consistent.

The jig 454 includes a hollow fixation member 466 and a platform 468 forcoupling a plurality of devices to the pelvis. The platform has agenerally T-shaped configuration including a first portion 468A coupledwith the proximal end of the fixation member 466 and a second portion468B disposed transversely to the first portion 468A. The first portion468A provides a support for a cradle 476 discussed further below. Thesecond portion 468B can include a plurality of docking devices 469 forcoupling directly or indirectly with the orientation device 172. TheT-shaped configuration provides the advantage that the docking devices469 can be disposed father away from the surgical site than is the casewith the system 100. This reduces any intrusion of the orientationdevice 172 into the working field.

In some cases, the fixation member 466 provides adequate stability inanchoring the system 450 to the pelvis. In other situations, the jig 454can be coupled with the pelvis from the second portion 468B. Forexample, a slot 470 can be formed in the second portion 468B on one orboth sides of location where the first portion 468A extends from thesecond portion 468B. The slots 470 can extend from a lateral edge of thesecond portion 468B toward location where the first portion 468A extendsfrom the second portion 468B. The slots 470 can include a plurality ofchannels 471 configured to receive fixation pins (e.g., Steinmann pins)that can be advanced into the pelvis. The channels 471 extend generallyparallel to the fixation member 466. The fixation pins can be securelyconnected to the second portion 468B in the channels 471 by a clampdevice 472. The clamp device can include a screw configured to draw theportions of the second portion 468B on either sides of the slot 470toward each other and thus to create large frictional forces on the pinsin the slots 471.

The slots 470 preferably are aligned such that a plane extends alongboth of the slots 470 along their length. Because the slots 470 are longand slender this plane can be readily visualized in an X-ray image. Itis preferred that the jig 454 be aligned to the pelvis such that theplane extending along the slots 470 is perpendicular to an axis of thepatient (e.g., the intersection of the medial lateral plane and thetransverse mid-plane of the patient). This feature provides a convenientway to visually confirm proper positioning of the jig 454 in oneembodiment.

The fixation member 466 includes a registration feature 473 and a foot474 adjacent to a distal end thereof and a coupling 475 adjacent to theproximal end thereof for connecting to the platform 468. The foot 474includes a plurality of spaced apart spikes extending from a distal endthereof capable of preventing or limiting rotation of the jig 454 whenthe fixation member 466 is connected to the pelvis. FIG. 17 shows thatsecuring the jig 462 to the pelvis can include positioning a pin orother bone engaging device through the fixation member 466. The pin andspikes extending from the foot 474 can provide three or more points ofcontact with the pelvis providing secure mounting of the jig 462.

The coupling 475 generally secures the platform 468 to the fixationmember 466. In some embodiment, the coupling 475 has a rotationalcapability that enables the platform to be positioned at selectivelocations about the longitudinal axis of the pin 466, for example toenable the platform 468 to be initially positioned in the correctorientation or to be moved during or after the procedure to make spacefor other surgical devices. One arrangement provides matching splinesthat extend parallel to the longitudinal axis of the fixation member466. This arrangement would permit splines on an upper portion of thecoupling 475 to be disengaged from splines on a lower portion of thecoupling 475. When disengaged, the platform 468 and the upper portion ofthe coupling 475 can be rotated relative to the lower portion of thecoupling 475. The splines can thereafter be re-engaged.

The jig 454 also preferably includes a cradle 476 that can be used tohold a probe arm 477. The cradle 476 includes a U-shaped recess having awidth between two upright members that is about equal to the width of anarm 477 of the landmark acquisition system 462. FIG. 17 shows the probearm 477 in a parked configuration as discussed above. If the sensor 204operates with components that are prone to accumulated error sources,the parked configuration can be used to eliminate such error. Asdiscussed above, the system 450 can be configured such that the positionand/or orientation of the sensor 204 relative to the orientation device172 is known. Thus, when the arm 477 is in the cradle 476 anyaccumulated error of components of the sensor 204 can be eliminated.

The cradle 476 can provide other convenient functions even if thesensing devices in the sensor 204 are not subject to sources ofaccumulated error. As discussed elsewhere herein, for confirmation ofaccuracy of the system or to provide a simplified reference frame notrequiring landmark acquisition, it may be desirable at some point of theprocedure to use the probe arm 477 and the sensor 204 to estimate theplane of the surgical table upon which the patient is resting. If, asdiscussed above, the plane intersecting the slots 470 is orientedperpendicular to the axis of the patient when the jig 454 is mounted tothe pelvis, the cradle will be parallel to the axis of the patient. Ifthe fixation member 466 is oriented vertically, the arm 477 will beparallel to the plane of the table when in the cradle 476. The system450 can thus use the plane of the table as a reference frame for guidingthe placement of the cup without registering landmarks. Or, the plane ofthe table can be used in combination with registering the anatomy aboutthe acetabular rim, as discussed above, to increase the accuracy ofnavigating the cup.

The cradle 476 also provides a convenient home position that keeps thearm 477 stationary and out of the way of other surgical instruments.FIG. 17A illustrates the probe arm 477 withdrawn from the cradle 476 andfree to move into contact with landmarks.

The jig 454 also includes a pivot feature 478 that is disposedhorizontally. FIG. 17B shows that the pivot feature 478 includes twohorizontal apertures 480. One of the apertures 480 is formed in the samestructure forming the cradle 476 but at an elevation below the cradle476. The other aperture 480 formed between the cradle 476 and aprojection of the fixation member 466. FIG. 17A shows that the probe arm477 is connected to the pivot feature 478 by a shaft 482 that extendsthrough the apertures. A movement device is provided between the shaft482 and the arm 477 to enable a distal tip of the arm to be rotatedabout perpendicular axes and to be advanced linearly relative to thestationary jig 454. One axis of rotation A of the movement device isdisposed parallel to and at an elevation above the platform 468. Anotheraxis of rotation B is disposed generally perpendicular to the axis A.Sliding of the arm 477 is enabled by a snug but sliding fit of the armin a housing C. By orienting the axis A in this manner, the sensitivityof accelerometers in the sensor 204 to small angular motions referencespoints about the acetabulum is heighted or maximized. This can enablelandmark acquisition with the system 450 based solely on accelerometers,which advantageously are not subject to accumulated error, which cansimplify the landmark acquisition process.

The registration feature 473 is a convenient way to enhance the accuracyof the sensor 204. In particular, in one variation of the methoddiscussed above, a distal tip of the probe arm 477 is brought intocontact with the registration feature 473. In one embodiment, theregistration feature 473 is a notch configured to receive andtemporarily retain the tip. Thereafter, the user can interact with theorientation device 172 to initialize accelerometers within the sensor204. Thereafter the points to be acquired can be sequentially contactedand the orientation and position of the sensor 204 can be sequentiallyrecorded in the system 450. Because the accelerometers are initializedclose to the points to be acquired, accuracy of the reading is enhancedas the angular error resulting from an error in the scale factor of theaccelerometers is minimized due to the small arc from the registrationfeature. For example, the jig 454 is configured to enable the landmarkacquisition assembly 458 to reach all points to be registered by movingless than about 45 degrees from an initial or home position in someembodiments. In other embodiments, the jig 454 is configured to enablethe landmark acquisition assembly 458 to reach all points to beregistered by moving less than about 25 degrees from the initialposition. In other embodiments, the jig 454 is configured to enable thelandmark acquisition assembly 458 to reach all points to be registeredby moving less than about 15 degrees from the initial position.

The jig 454 also is configured to interact well with the soft tissuethat is disposed around the surgical site in the posterior approach. Inthis approach, an incision is made in soft tissue that is kept as smallas possible. In one approach, the fixation member 466 is positioned atthe end of the incision. Where the incision is made as minimal aspossible, the jig 454 can also function as a retractor. The T-shapedconfiguration is particularly well suited for this function because thefirst portion 468A of the platform 468 can be received between themiddle and ring fingers of the user with the second portion 468B in thepalm of the hand. With the foot 474 gripping the pelvis, the jig 454 canbe tilted from the platform 468 away from the hip joint to retract thetissue away.

FIGS. 17C-1 and 17C-2 illustrate further embodiments of a posteriorapproach jig 454A having a mounting device 488 disposed adjacent to thedistal end of a fixation member 466A, which is otherwise similar to thefixation member 466. The fixation member 466A includes a tubular body490 coupled with the fixation member 466A, which in this embodiment actsas a primary fixation member. The tubular body 490 extends along a lumenthat is angled relative to the lumen of the fixation member 466A. Thelumen in the tubular body 490 is configured to accept a fixation pin 492that can be driven into the bone, as illustrated in FIG. 17C-2 at anoblique angle. The fixation pin 492 supplements the fixation provided bythe fixation member 466A. The fixation pin 492 can be used inconjunction with the optional long pin(s) extending through the channels471, e.g., into the ilium or as a substitute for that option. Thefixation pin 492 has the advantage of not requiring any additional holesin the skin because it is located within the primary incision made toaccess the joint in the procedure. The fixation pin 492 can be threadedto engage the bone in one embodiment. In some embodiments, a lockingdevice 494 can be provided to secure the pin 492 in the lumen of thetubular body 490. A set screw is one example of a locking device 494that can be used. The locking device 494 enables the fixation pin 492 tobe headless, which avoids issues with screw threads stripping the holein the bone into which the pin 492 is inserted.

3. Posterior Approach: Workflow Considerations

As noted above, a workflow problem arises in typical hip replacementprocedures in that anatomical features that can be more easilyreferences are unavailable in the traditional posterior approach foroperating on the joint.

By performing a CT-based study of a large number of human pelvises, theassignee of this application has been able to calculate apopulation-based average relationship between multiple planes created byvarious points in, on or around the acetabulum that are accessibleduring posterior approach hip replacement (each plane, an “AcetabularPlane”), and the Anterior Pelvic Plane. One of the key features ofposterior hip navigation for some embodiments disclosed herein is theability of a module, e.g., software incorporated into a processor, whichmay be on a computer, or one or both of the orientation device 172 andsensor 204, to calculate a transformation from one reference frame toanother. As described in more detail elsewhere herein, several pointsare referenced in, on or around the acetabulum and from these points aproxy Acetabular Plane is calculated.

Next, in certain embodiments described herein a module operable toprocess an algorithm, e.g., by executing software in one or both of theorientation device 172 and sensor 204 alone or with a separate computer,is able to calculate a transformation from the proxy Acetabular Plane toAnterior Pelvic Plane. The approach indirectly registers the AnteriorPelvic Plane without requiring a direct supine registration andsubsequent patient movement and re-draping necessary in standardnavigation. A module in certain embodiments described herein is thenable to provide the user real time navigation data of the orientation ofa hip instrument (e.g., the impactors 300, 300A) with respect to theAnterior Pelvic Plane.

In certain systems described herein, a further advantage is that thesystems are able to implement the plane transformation algorithm tocalculate an Anterior Pelvic Plane from one of any number of proxyAcetabular Planes that the surgeon chooses to register. This enables thesurgeon to have greater flexibility in Acetabular Plane landmarkselection to take into account the quality or accessibility of certainlandmarks. For example, in cases of minimal deformity around theacetabular rim, the surgeon may choose to register landmarks around therim, which are easily accessible. In cases where there is greatdeformity or high presence of osteophytes on the acetabular rim, thesurgeon may instead choose to register an Acetabular Plane based onextra-acetabular landmarks (or described as “off-rim” elsewhere herein)outside of the rim that are unaffected by disease or prior hipreplacement surgery.

Examples of anatomical landmarks that may be used to create a proxyAcetabular Plane and that are shown in FIG. 2 include but are notlimited to:

Extra-acetabular landmarks (Ischium/Ilium/Pubis)

-   -   (A) The lowest point of the acetabular sulcus of the ischium    -   (B) The prominence of the superior pubic ramus    -   (G) The confluence of the anterior inferior iliac spine (AIIS)        and the outer border of the acetabular rim

Acetabular Rim Landmarks

-   -   (E) The center of the anterior insertion of the trans-acetabular        ligament    -   (F) The center of the posterior insertion of the        trans-acetabular ligament    -   (H) The most superior point of the acetabular rim.

Additional points can be combined with either of the groups of pointslisted above. For example, in one embodiment, point “D” is used. Point Dis the midpoint of the inferior border of the acetabular notch. Asdiscussed in connection with FIG. 36 below, point D corresponds to thebottom landmark 380B used to form the line 382. Point D is used in thatapproach to provide patient specific refinements to the positioning.

A further key benefit of certain embodiment discussed herein is that theforegoing plane transformation capabilities increase the accuracy of thetransformation between the proxy Acetabular Plane registered and theAnterior Pelvic Plane above the general population average data by theuser inputting certain patient-specific information, such as gender.

Additionally, certain embodiments of systems including one or more ofthe orientation device 172, sensor 204, or a separate computer may havemodules that are operable, e.g., by processing software, to allow theuser to input an angular or plane relationship between an proxyAcetabular Plane and Anterior Pelvic Plane that the surgeon measuredbased on pre-operative imaging, allowing for a partial or whole planetransformation based on patient-specific data rather than populationdata. By way of example, the surgeon may choose to pre-operativelymeasure an angle created by (a) landmarks that are both visible on anA/P pelvis x-ray and that can be referenced during posterior hipreplacement, and (b) landmarks that are both visible on the pelvis x-rayand that are directly associated with inclination measurement in theAnterior Pelvic Plane. If this angular relationship is inputted into amodule of a system including one or more of the orientation device 172,the sensor 204, or a separate computer, which module is capable ofmaking calculations processing software and the surgeon registers thelandmarks described in (a), inclination navigation will be basedspecifically on that patient rather than a population average. Landmarks(D) and (H) listed above are examples of landmarks that are both visibleon an A/P pelvis x-ray and that can be referenced to create a proxyAcetabular Plane in posterior hip replacement.

These aspects of the systems adapted for posterior approach hip jointreplacement can greatly enhance both workflow and accuracy in suchprocedures.

4. Posterior Approach: Further Systems with an Orientation SensingDevice and Camera

FIG. 18 shows a hip navigation system 600 adapted to navigate a hipjoint procedure with reference to anatomical landmarks. The system 600is shown mounted on a pelvis in a posterior approach in FIG. 18. FIG. 18shows an early phase of a procedure prior to the joint being dislocatedbut after the system 600 is mounted to the pelvis. The system 600 can beadapted for various techniques. As discussed further below, suchvariations involve registering the femur prior to and after the joint isreplaced to confirm an aspect of the relative position and/ororientation of the femur, e.g., leg length, joint offset, and rotationalorientation of the femoral neck. The system 600 can include anycomponent described herein. The system 600 can be used in any techniqueor method step described herein.

The system 600 can include a fixation base 602, a first assembly 604 anda second assembly 606. The first assembly 604 is rigidly connected tothe hip in the illustrated configuration so that motion of the hip causecorresponding motion of sensor(s) in the first assembly 604 as discussedbelow. Sensing this motion enables the system 600 to eliminate movementof the patient as a source of error in the navigation. The secondassembly 606 provides a full range of controlled motion and sensor(s)that are able to track the motion, in concert with sensor(s) in thefirst assembly 604. Additional details of systems, devices, sensors, andmethods are set forth in U.S. Pat. No. 8,118,815; US US2010/0076505; andU.S. Pat. No. 8,057,479 which are all incorporated by reference hereinin their entireties for all purposes. The sensors in assemblies 604, 606preferably transfer data among themselves and in some cases withexternal devices and monitors wirelessly, using Bluetooth, Wifi® orother standard wireless telemetry protocol.

The system 600 can include one or more fixation pins. In the illustratedembodiment, a first fixation pin 610 and a second fixation pin 612 areshown. Other configurations are contemplated (e.g., one fixation pin,three fixation pins, four fixation pins, etc.). The fixation pins 610,612 can be elongate structures. FIG. 19 shows the fixation pin 610. Insome embodiments, the fixation pins 610, 612 are identical orsubstantially similar. In some embodiments, the fixation pins 610, 612are different and can be adapted to be inserted into different anatomiclocations.

The fixation pin 610 can be substantially cylindrical, as shown in FIG.19. The fixation pin 610 can have a distal end 614 that can be advancedto a pelvic bone at an anatomical location or landmark or other selectedlocation. In the illustrated embodiment, the distal end 614 is threaded.The distal end 614 can include a sharpened tip designed to penetratebone. The fixation pin 610 can have a proximal end 616. The proximal end616 can include attachments features to couple the fixation pin 610 witha driver. In the illustrated embodiment, the proximal end 616 includes atri-flat shape designed to couple with a tri-flat socket. The fixationpin 610 can include one or more markings along the length of thefixation pin 610. The markings can indicate the orientation of thefixation base 602 relative to the fixation pin 610.

Referring back to FIG. 18, each fixation pin 610, 612 can be driven intothe ilium on the pelvis. As discussed further below, each fixation pin610, 612 can be coupled with other bones in other techniques. Forexample, one of the fixation pins 610, 612 can be coupled with theischium or the pubis. In some techniques, one of the fixation pins 610,612 is mounted to a pelvic bone but not at a landmark. One of thefixation pins 610, 612 can be coupled at a point superior to thesuperior-most point on the acetabular rim. In some techniques, one ofthe fixation pins 610, 612 is about 10 mm above the superior-most pointon the acetabular rim. In some techniques, three or more anatomicallandmarks disposed about the acetabulum can be acquired, as discussedbelow. When one of the fixation pins 610, 612 is coupled with alandmark, only two additional landmarks are acquired in some embodimentsas discussed below. One reason for mounting the fixation pins 610, 612away from the landmarks is that the landmarks may not be visible oraccessible before dislocating the hip joint. If the clinician wishes touse the system 600 to reference the femur as discussed below, it may berequired to mount the fixation pins 610, 612 away from the landmarks.

The system 600 can include the fixation base 602 shown in FIGS. 20A-20H.The fixation base 602 can function as a clamp with the one or morefixation pins 610, 612. FIG. 20A shows an exploded view of the fixationbase 602. FIGS. 20B-20D show other views of the fixation base 602. Thefixation base 602 can include a platform 620 and a support 622. Theplatform 620 can interact with the support 622 to function as a clamp.In the illustrated embodiment, the fixation base 602 can include one ormore fixation devices 624. In the illustrated embodiment, two fixationdevices are shown but other configurations are contemplated (e.g., one,three, four, etc.). The fixation devices 624 can include one or morethreaded sections. In the illustrate embodiment, the fixation devices624 are screws with a head and a threaded shank. The platform 620 caninclude one or more holes. The support 622 can include one or moreholes. The fixation devices 624 can pass through or engage one or moreholes in the support 622. In some embodiments, each hole in the support622 is threaded. The fixation devices 624 can pass through or engage oneor more holes in the platform 620. In some embodiments, each hole in theplatform 620 is threaded. Rotation of the fixation devices 624 can causethe support 622 to move toward the platform 620 and/or the platform 620to move toward the support 622.

The platform 620 and the support 622 form one or more channelstherebetween, as shown in FIG. 20C. The number of channels cancorrespond to the number of fixation pins. In the illustratedembodiment, a first channel 626 and a second channel 628 are shown. Thechannels extend from a top surface of the platform 620 and/or thesupport 622 to a bottom surface of the platform 620 and/or the support622. The channels 626, 628 extend in a direction transverse to thedirection of the fixation devices 624 when the fixation devices 624 areengaged with the platform 620 and the support 622. The first channel 626is sized to accept the first fixation pin 610 and the second channel 628is sized to accept the second fixation pin 612. Rotation of the fixationdevices 624 can cause the support 622 to move toward the platform 620.The channels 626, 628 can decrease in diameter with the rotation of thefixation devices 624. Upon rotation of the fixation devices 624, eachfixation pin 610, 612 is retained between the platform 620 and thesupport 622. The fixation base 602 can include divot 630. The divot 630can be associated with a parked configuration or home position, asdescribed herein. The divot 630 is an example of a registration featuredisposed on the system 600.

The fixation base 602 can include a first coupler 632. The first coupler632 can couple to one or more components of the system 600. In someembodiments, the first coupler 632 is a universal coupler. The firstcoupler 632 can include an elongate post 635. In some embodiments, thefirst coupler 632 can have a regular shape (e.g., cylindrical). In someembodiments, the first coupler 632 can have an irregular shape (e.g.,triangular, teardrop, elliptical, rectangular). The irregular shape mayfacilitate alignment of other components of the system 600 with theplatform 620 of the fixation base 602. In the illustrated embodiment,the other components of the system 600 can mate with the first coupler632 in a single orientation.

The first coupler 632 can include a slot 634. The slot 634 can betransverse to the longitudinal axis of the first coupler 632. The slot634 can form an angle with an axis transverse to the longitudinal axis.This angle can be approximately 10°, between 5° and 15°, between 0° and20°, etc. The slot 634 can be designed to interact with detents of othercomponents of the system 600, as described herein. The first coupler 632can include a tapered surface 636. The tapered surface 636 canfacilitate entry of the first coupler 632 within other components of thesystem 600. The tapered surface 636 can move the detent of othercomponents of the system 600 when the first coupler 632 is inserterwithin the other component. As shown in FIG. 20A, the first coupler 632can include the elongate post 635 coupled to a hole on the top surfaceof the platform 620. As shown in FIG. 20E, in an alternative embodiment,the first coupler 632A is integrally formed with the platform 620. Apost 632B can be inserted from a bottom surface of the platform 620 tosupport the first coupler 632A.

The system 600 can include the first assembly 604 shown in FIGS.21A-21G. The first assembly 604 can include a pelvic bracket 638. In theillustrated embodiment, the pelvic bracket 638 can be substantiallyvertical in use, as shown in FIG. 18. The first assembly 604 can bedesigned to couple with the first coupler 632 of the fixation base 602.The first assembly 604 can include a lock lever 640. The lock lever 640can be coupled to the pelvic bracket 638 with pivot pins. The lock lever640 can be pivoted relative to the pelvic bracket 638. In someembodiments, the tapered surface 636 of the first coupler 632 causes thepivoting of the lock lever 640. In some embodiment, the surgeon causesthe pivoting of the lock lever 640. The lock lever 640 can include adetent 642. The detent 642 is sized and shaped to be received within theslot 634. The engagement of the detent 642 and the slot 634 can rigidlycouple the first assembly 604 with the fixation base 602.

The first assembly 604 can include an extension 644. The extension 644can be coupled to the pelvic bracket 638. The extension 644 can includea mount 646 designed to couple with the surgical orientation device 172.In the illustrated embodiment, the mount 646 includes a lock and releaselever that can pivot relative to the extension 644. The surgicalorientation device 172 can include features to mate with the lock andrelease lever (not shown). Other configurations are contemplated. Thesurgical orientation device 172 is rigidly coupled to the extension 644when engaged with the mount 646. The surgical orientation device 172 canbe angled when coupled to the first assembly 604, as shown in FIG. 18.The surgical orientation device 172 can be angled approximately 35° fromthe horizontal axis. Other angles from the horizontal axis arecontemplated, (e.g., 5°, 10°, 15°, 20°, 25°, 30°, 40°, 45°, 50°, 55°,60°, 65°, 70°, 75°, 80°, or 85°, between 30°-40°, between 25°-45′). Insome embodiments, the angle of the surgical orientation device 172improves visibility. The angle is a compromise between tilting thesurgical orientation device 172 up toward the surgeon and allowinganother surgeon or surgical assistant on the other side of the patientto still see the display. One reason for angling the surgicalorientation device 172 is that in an anterior approach, the surgeonstands toward the patient's feet while impacting the acetabular implantand a horizontal display would be difficult to see.

The surgical orientation device 172 detects orientation and rotation ofthe device 172 relative to a reference frame. The surgical orientationdevice 172 preferably comprises at least one sourceless sensor, such asan accelerometer, a gyroscope, or a combination of these sensors andother sensors. In some embodiments, the surgical orientation device 172includes a three axis accelerometer to detect orientation relative togravity and a plurality of gyroscopes to detect rotation. Other sensorscould be used in various modifications. Examples of specific sensorcombinations include Analog Devices ADIS 16445 and Invensense MPU-6050or MPU-9150 among others. In some approaches, the surgical orientationdevice 172 can be disposable and so the sensors preferably are lessexpensive sensors. In some embodiments, the surgical orientation device172 is disposable.

The extension 644 can include a second coupler 648. In some embodiments,the second coupler 648 is a universal coupler. The second coupler 648can be substantially similar to the first coupler 632 described herein.The second coupler 648 can be designed to couple with the secondassembly 606. The couplers 632, 648 are designed to secure to othercomponents of the system 600 in a secure but releasable manner. Theengagement between the coupler 632 and the first assembly 604 minimizesor prevents relative movement therebetween to avoid any mechanicalrelative movement during navigation procedures so that movement of thesurgical orientation device 172 corresponds to movement of the hip. Thesecond coupler 648 provides a stable manner to position the secondassembly 606 relative to the first assembly 604.

The system 600 can include the second assembly 606 shown in FIG.22A-22F. The second assembly 606 can include a probe bracket 652. In theillustrated embodiment, the probe bracket 652 can be substantiallyangled with respect to the pelvic bracket 638 when in use, as shown inFIG. 18. The second assembly 606 can be designed to couple with thesecond coupler 648 of the first assembly 604. The second assembly 606can include a lock lever 654. The lock lever 654 can be coupled to theprobe bracket 652 with pivot pins. The lock lever 654 can be pivotedrelative to the probe bracket 652. In some embodiments, the taperedsurface of the second coupler 648 causes the pivoting of the lock lever654. In some embodiment, the surgeon causes the pivoting of the locklever 654. The lock lever 654 can include a detent 656. The detent 656is sized and shaped to be received within the slot of the second coupler648. The engagement of the detent 656 and the slot can rigidly couplethe second assembly 606 with the first assembly 604.

In the illustrated embodiment, the second assembly 606 includes a mount658. The mount 658 can be coupled to the probe bracket 652 to allowrelative movement therebetween. The mount 658 can be received within anopening in the probe bracket 652. The mount 658 can permit rotationabout a longitudinal axis of the mount 658 relative to the probe bracket652.

The second assembly 606 can include a dock 662. The dock 662 can becoupled to the mount 658 to allow relative movement therebetween. Thedock 662 can be coupled to the mount 658 with one or more pivot pins660. The dock 662 can have two degrees of freedom relative to the probebracket 652 (e.g., rotational motion and pivoting motion). The dock 662can include a sliding support with a through lumen 664. The throughlumen 664 is sized to accept a probe 678. The probe 678 has a distal end680 designed to touch locations, as described herein. The distal end 680can be straight as shown in FIG. 22A. In other embodiments, the distalend 680 is slanted or curved, e.g., as shown in FIGS. 4 and 17.

The through lumen 664 of the dock 662 permits slideable extension of theprobe 678. The dock 662 is movable relative to the probe bracket 652(e.g., via rotation of the mount 658 and pivoting of the pivot pin 660).The dock 662 can be rotated about a longitudinal axis of the mount 658to different rotational positions relative to the attachment location ofthe fixation pins 610, 612. This may require movement of the mount 658in a rotational manner relative to the probe bracket 652. The dock 662can be pivoted about the longitudinal axis of the pivot pins 660 todifferent positions relative to the attachment location of the fixationpins 610, 612. This may require movement of the dock 662 in a pivotingmanner relative to the mount 658.

The probe 678 can be coupled to the dock 662 such that the probe 678 ismovable relative to the probe bracket 652 (e.g., via rotation of themount 658 and pivoting of the pivot pin 660). This maneuverabilityenables the distal end 680 of the probe 678 to pivot or rotate tocontact anatomical landmarks, as discussed herein. The probe 678 can beslid relative to the dock 662 to different translational positionsrelative to the attachment location of the fixation pins 610, 612. Theslidability of the probe 678 within the dock 662 enables the distal end680 to move to reach anatomical landmarks in the same plane of the probe678 but closer to or farther from the distal end 680.

The second assembly 606 permits a range of motion of a distal end 680 ofthe probe 678 to facilitate acquiring a plurality of landmarks that aredifferent distances from the attachment location of the fixation pins610, 612, as discussed further below. In other words, the distal end 680of the probe 678 can be extended away from the axis of the slidingsupport of the dock 662 or can be retracted to a position closer to theaxis of the sliding support of the dock 662.

The dock 662 can include a third coupler 668. In some embodiments, thethird coupler 668 is a universal coupler. In some embodiments, the thirdcoupler 668 is identical or substantially similar to the second coupler648. This permits the orientation sensing device 204 to couple to eitherthe second coupler 648 or the third coupler 668, as described herein. Insome embodiments, the third coupler 668 can be substantially similar tothe first coupler 632 described herein. The third coupler 668 can bedesigned to couple with the orientation sensing device 204. FIG. 23A-23Cillustrate an embodiment of the orientation sensing device 204. Thesecond assembly 606 can include an extension 670. The extension 670 cancouple to the third coupler 668 of the dock 662. The engagement betweenthe third coupler 668 and the extension 670 minimizes or preventsrelative movement therebetween to avoid any mechanical relative movementduring navigation procedures. The extension 670 can include a mount 672designed to couple with the orientation sensing device 204. In theillustrated embodiment, the mount 672 includes a lock and release leverthat can pivot relative to the extension 670. The orientation sensingdevice 204 can include features to mate with the lock and release lever.Other configurations are contemplated. The orientation sensing device204 is rigidly coupled to the extension 670 when engaged with the mount672.

The orientation sensing device 204 can be angled when coupled to thesecond assembly 606, as shown in FIG. 18. The orientation sensing device204 can be angled approximately 35° from the horizontal axis. Otherangles from the horizontal axis are contemplated, (e.g., 5°, 10°, 15°,20°, 25°, 30°, 40°, 45°, 50°, 55°, 60°, 65°, 70°, 75°, 80°, or 85°,between 30°-40°, between 25°-45°). In some embodiments, the angle of theorientation sensing device 204 improves visibility.

The orientation sensing device 204 detects orientation and rotation ofthe probe 678, as described herein. The orientation sensing device 204preferably comprises at least one sourceless sensor, such as anaccelerometer, a gyroscope, or a combination of these sensors and othersensors. In some embodiments, the orientation sensing device 204includes a three axis accelerometer to detect orientation relative togravity and a plurality of gyroscopes to detect rotation. Other sensorscould be used in various modifications. In some embodiments, theorientation sensing device 204 is reusable.

Referring back to FIGS. 22A and 22C, the probe 678 can include a marking682. The marking 682 can indicate length or extension of the probe 678relative to the dock 662. The marking 682 can include a scale. In someembodiments, the marking 682 can be over a range of from about 8 inches,10 inches, 12 inches, approximately 8-12 inches, etc. The marking 682can be printed on the probe 678. In some embodiments, the marking 682can be on a separate component such as a probe inlay 676. The probeinlay 676 can be received within a portion of the probe 678. In someembodiments, the probe inlay 676 is separated a distance from the distalend 680 of the probe 678.

Referring to FIG. 23C, the system 600 can include a camera 684. Thecamera 684 can capture images of the marking 682. In some embodiments,the camera 684 and/or the orientation sensing device 204 can include alight to illuminate the marking 682. In some embodiments, the light is aLED. In some embodiments, the dock 662 includes a window to permit thecamera 684 to capture images. In other embodiments, the camera 684captures images of the marking 682 extending beyond the dock 662. Thecamera 684 can read the marking 682 to provide accurate determination ofthe translational position of the probe 678 relative to the dock 662.This can enable one of the sensors in the orientation sensing device 204to be eliminated or inactivated. In another embodiment, camera dataderived from the marking 682 can be used to confirm the data fromsensors in the orientation sensing device 204.

In some embodiments, the camera 684 is integrally formed with theorientation sensing device 204. In some embodiments, the camera 684 is aseparate component from the orientation sensing device 204. The camera684 can be held in a fixed position relative to the dock 662. Themarking 682 can be positioned on the probe 678 beneath the camera 684when the probe 678 is positioned within the through lumen 664. Thecamera 684 can be directly above the marking 682. The camera 684 can befixed relative to the through lumen 664 of the dock 662. The dock 662,the camera 684 and the orientation sensing device 204 can move as a unitto allow positioning of the probe 678. One advantage of orienting theorientation sensing device 204 as illustrated in system 600 is improvedvisibility. The lower-profile construct is less likely to obstruct theuser's view. One advantage of orienting the orientation sensing device204 as illustrated in system 600 is ease of manufacturing. The camera684 can be mounted flush on the circuit board. The correspondingtransparent window (not shown), which can allow the camera 684 tocapture images, in the housing of the orientation sensing device 204 isoriented in the direction of the mold pull. The shorter distance to themarking 682 also better accommodates the available camera, which has ashort focal length. In some embodiments, the camera 684 captures animage though a lumen (not shown) in the dock 662. One advantage ofhaving the camera 684 read the marking 682 through the lumen is thisshields the camera 684 from outside light sources. Light, such as ORlight, may interfere with the camera function such as the function ofcapturing an image of the marking 682. In other embodiments, the camera684 may incorporate a shroud feature to block ambient light. In someembodiments, the camera 684 is pointed downward from a back side of theorientation sensing device 204. In some embodiments, the orientationsensing device 204 shields camera 684 from light.

The system 600 can include a femur tracker 686 as shown in FIG. 24A-24B.The femur tracker 686 can be coupled to the femur as shown in FIG. 18.The femur tracker 686 can be used to track the position of the femurduring the procedure. The femur tracker 686 can include one or morefixation structures. In the illustrated embodiment, the fixationstructures are holes 688. The holes 688 are sized to permit a fastenertherethrough (e.g., a screw, pin, k-wire, etc.). The femur tracker 686can include one or more points 690. The points 690 can include Points A,B, C as described herein and shown in FIG. 24A. The femur tracker 686can include three points 690. Other configurations are contemplated(e.g., one point, two points, four points, five points, etc.). Thepoints 690 can include divots as shown in FIG. 24A. The points 690 caninclude markings. The femur tracker 686 can provide more consistent andrepeatable results than a marking the femur. The femur tracker 686 canprovide points 690 which are fixed relative to the femur. The femurtracker 686 can provide multiple points 690. One advantage toregistering multiple points on the femur is that the software in thesurgical orientation device 172 can then correct for changes in thefemur angle with respect to the pelvis between the baseline measurementand the later measurement. The baseline measurement can be apreoperative measurement. The later measurement can be after the shellis positioned in the acetabulum. In some embodiments, the points 690 arelocated on the femur tracker 686. In some embodiments, one or morepoints are marks located directly on the femur Fm and one or more pointsare located on the femur tracker 686. In some embodiments, one or morepoints are marks located directly on the femur Fm. One advantage tousing a femur tracker 686 is that the marks are easier to find forrepeat registrations. One advantage to using a femur tracker 686 is thatspacing the points 690 at known distances from each other allowssoftware checks to verify that the correct points 690 are registered inthe right sequence. One advantage to using a femur tracker 686 is thatspacing the points 690 at known distances from each other allowssoftware checks to verify that the femur and the pelvis have not movedin between point registrations. One advantage to using marks locateddirectly on the femur Fm is that the components are not affixed to thefemur. The marks do not require any drill holes or fasteners. This mayprevent future fractures or damage to the proximal end of the femur. Thefemur tracker 686 can be a unitary structure. The femur tracker 686 canbe a low profile component. The femur tracker 686 can be coupled to thefemur throughout the procedure. The femur tracker 686 can form a smoothsurface preventing the femur tracker 686 from hooking soft tissue. Thefemur tracker 686 can form a smooth surface preventing the femur tracker686 from loosening in the bone.

FIG. 18 illustrates a parked configuration or home position of the probe678. In some embodiments, a portion of the distal end 680 is moved intoengagement with the platform 620. In some techniques, the distal end 680of the probe 678 engages the divot 630 of the platform 620. The parkedconfiguration enables the navigation system 600 to manage errors thatcan compound in some inertial sensors. For example, the parkedconfiguration advantageously includes the ability to position and holdthe devices 172, 204 stable for substantially no relative movement. Alsothe relative position of the sensors in the devices 172, 204 whencoupled with the first and second assemblies 604, 606 can be known fromthe geometry of the first assembly 604 and the second assembly 606. Forexample, in one embodiment, gyroscopic sensors in the surgicalorientation device 172 and in the orientation sensing device 204 can besynchronized when a stable and known orientation is detected and one ormore of the gyroscopes, e.g., the gyroscope in the orientation sensingdevice 204, can be zeroed after that condition is met. Furthertechniques employing the parked configuration will be discussed furtherbelow.

At the surgeon's discretion the system 600 can be used to navigate acondition of the femur prior to hip replacement. The orientation sensingdevice 204 can be initialized or zeroed such as by placing it back inthe parked configuration on the platform 620 as in FIG. 18. Thereafter,the distal end 680 of the probe 678 can be brought into contact with thepoints 690. The orientation sensing device 204 can be stationaryrelative to the dock 662. The surgical orientation device 172 can bestationary relative to the pelvis. The surgical orientation device 172can be signaled to record the orientation of the orientation sensingdevice 204. The camera 684 can record the extension of the probe 678relative to the dock 662. The distance from the camera 684 to the distalend 680 of the probe 678 or the distance from the system 600 to theanatomy being registered can then be recorded in the surgicalorientation device 172. The position can be based on reading by thecamera 684 of the marking 682. The distance can be capturedautomatically by the camera 684. In other embodiments, the user reads ameasurement from the marking 682 and inputs the distance into thesurgical orientation device 172.

The system 600 can include features that provide notable advantages forthe surgeon. The system 600 can include modular instruments. In someembodiments, the fixation base 602 can include a low profile platform620 and a low profile support 622. The low profile fixation base 602 canprevent the obstruction of the surgical field. The fixation base 602 canbe easily removed when not in use. The clamping action between theplatform 620 and the support 622 allow the fixation base 602 to beeasily removed from the fixation pins 610, 612. In the illustratedembodiment, rotation of the fixation devices 624 can cause the support622 to move away from the platform 620. The channels 626, 628 canincrease in diameter. The platform 620 and the support 622 can bedecoupled from the fixation pins 610, 612.

The one or more fixation pins 610, 612 can be spaced apart from oneanother. This can permit the fixation pins 610, 612 to be driven intodifferent locations on the anatomy of the patient. In the illustratedembodiment, two fixation pins 610, 612 are provided. The utilization oftwo or more fixation pins may provide more stability for the fixationbase 602. The fixation pins 610, 612 allow the surgeon much moreflexibility when anchoring the system 600. The surgeon has flexibilityin the location and/or depth of placement. The surgeon can optimize thepenetration angle. In some techniques, the surgeon can enter the bonemore perpendicularly. The fixation pins 610, 612 can be placed inlocations to avoid sensitive anatomical structures.

The system 600 can include one or more couplers. The system 600 caninclude the first coupler 632 coupled to the platform 620 of thefixation base 602. The first coupler 632 can couple the fixation base602 to the first assembly 604 as shown in FIG. 18. The first coupler 632can couple the fixation base 602 to any other component of the system600. The system 600 can include the second coupler 648 coupled to thefirst assembly 604. The second coupler 648 can couple the first assembly604 to the second assembly 606 as shown in FIG. 18. The second coupler648 can couple the first assembly 604 to the extension 670 as describedherein. The second coupler 648 can couple the first assembly 604 to anyother component of the system 600. The system 600 can include the thirdcoupler 668 coupled to the dock 662 of the second assembly 606. Thethird coupler 668 can couple the dock 662 to the extension 670 as shownin FIG. 18. The third coupler 668 can couple the second assembly 606 toany other component of the system 600.

Other tools or assemblies, such as the tools and assemblies describedherein can include one or more couplers. The couplers allow componentsto rigidly couple. In some embodiments wherein the couplers have anirregular shape, the couplers can couple components in a singleorientation. The slot of the couplers, such as slot 634 of the firstcoupler 632, can be angled relative to the horizontal axis. This canprevent inadvertent detachment of the components from the couplers.

The system 600 can include the camera 684. The camera 684 can be acomponent of the orientation sensing device 204. The orientation sensingdevice 204 can be coupled to the dock 662 with the third coupler 668.The camera 684 can be in a fixed location relative to the probe 678. Thecamera 684 can remain fixed in position as the probe 678 is moved. Thecamera 684 can be oriented such that the camera 684 faces the marking682. In addition, the orientation sensing device 204 can be in a fixedlocation relative to the probe 678. The orientation sensing device 204can remain fixed in position as the probe 678 is moved. The orientationsensing device 204 can be oriented such that a flat back side of theorientation sensing device 204 faces the marking 682.

The camera 684 can capture an image of the marking 682. The image cancorrespond with a distance of the probe 678. The distance changes as theprobe 678 slides through the through lumen 664 of the dock 662. In someembodiments, the camera 684 can read a binary code of the marking 682.In some embodiments, the camera 684 can read a scale or other markings.The camera 684 can be positioned directly over the marking 682.

The distance related to the extension of the probe 678 can be used inconjunction with the orientation and positional data from theorientation sensing device 204. The surgical orientation device 172 canuse the length measurement from the camera 684 and the data from theorientation sensing device 204 to determine the location of the distalend 680 of the probe 678.

FIGS. 25A-25C show a hip navigation system 600A adapted to navigate ahip joint procedure with reference to anatomical landmarks. The system600A is shown mounted on a pelvis in a posterior approach in FIGS.25A-25C. The system 600A can include any of the features described abovewith reference to system 600 and any component described herein. Thesystem 600A can be used in any technique or method step describedherein. As one example, the system 600A can include the surgicalorientation device 172 described herein. As another example, the system600A can include the orientation sensing device 204 described herein. Asan example, the system 600A includes a camera 684 described herein.

The system 600A can include a fixation base 602A, a first assembly 604Aand a second assembly 606A. The first assembly 604A is rigidly connectedto the hip in the illustrated configuration so that motion of the hipcause corresponding motion of sensor(s) in the first assembly 604A asdiscussed below. Sensing this motion enables the system 600A toeliminate movement of the patient as a source of error in thenavigation. The second assembly 606A provides a full range of controlledmotion and sensor(s) that are able to track the motion, in concert withsensor(s) in the first assembly 604A.

The system 600A can include the fixation base 602A as shown in FIGS.26A-26C. The fixation base can include a platform 620A. The platform620A can include one or more holes 611A. The holes 611A can be sized toaccept a fastener 613A to secure the fixation base 602A to the bone,shown in FIG. 25B. The platform 620A can include one or more spikes615A. The spikes 615A can secure the fixation base 602A to the bone. Thefixation base 602A can include divot 630A. The divot 630A can beassociated with a parked configuration or home position, as shown inFIG. 25B. The divot 630A can be a registration feature of the system600.

Referring to FIG. 25B, each fastener 613A can be driven into the iliumon the pelvis. As discussed further below, each fastener 613A can becoupled with other bones in other techniques. For example, one of thefasteners 613A can be coupled with the ischium or the pubis. In sometechniques, one of the fasteners 613A is mounted to a pelvic bone butnot at a landmark. One of the fasteners 613A can be coupled at a pointsuperior to the superior-most point on the acetabular rim. In sometechniques, one of the fasteners 613A is about 10 mm above thesuperior-most point on the acetabular rim. In some techniques, three ormore anatomical landmarks disposed about the acetabulum can be acquired,as discussed below. When one of the fasteners 613A is coupled with alandmark, only two additional landmarks are acquired in some embodimentsas discussed below. One reason for mounting the fastener 613A away fromthe landmarks is that the landmarks may not be visible or accessiblebefore dislocating the hip joint. If the clinician wishes to use thesystem 600A to reference the femur as discussed below, it may berequired to mount the fasteners 613A away from the landmarks.

The fixation base 602A can include the first coupler 632. The firstcoupler 632 can couple to one or more components of the system 600A. Thesystem 600A can include the first assembly 604A shown in FIGS. 25A-25B.The first assembly 604A can include a pelvic bracket 638A. In theillustrated embodiment, the pelvic bracket 638A can be substantiallyvertical in use, as shown in FIG. 25A. The first assembly 604A can bedesigned to couple with the first coupler 632 of the fixation base 602A.The pelvic bracket 638A of system 600A can be longer than the pelvicbracket 638 of system 600.

The system 600A can include the second assembly 606A shown in FIG. 25A.The distal end 680A of the probe 678A can pivot or rotate to contactanatomical landmarks, similar to probe 678A described herein. The distalend 680 can be angled, slanted or curved. The curvature of the distalend 680A of the probe 678A can facilitate the acquisition of landmarksor other points as described herein. The probe 678A can be slid todifferent translational positions relative to the attachment location ofthe fixation base 602A. The second assembly 606A permits a range ofmotion of a distal end 680A of the probe 678A to facilitate acquiring aplurality of landmarks that are different locations from the attachmentlocation of the fixation base 602A.

The system 600A can include a femur tracker 686A as shown in FIG. 25C.The femur tracker 686A can be coupled to a femur base 687A as shown inFIG. 25C. The femur tracker 686A can be used to track the position ofthe femur during the procedure. The femur base 687A can include one ormore fixation structures. In the illustrated embodiment, the fixationstructures are holes 688A shown in FIG. 28C. The holes 688A are sized topermit a fastener therethrough (e.g., a screw, pin, k-wire, etc.). Thefemur base 687A can include spikes 685A as shown in FIGS. 28A-28B. Thespikes 685A can anchor the femur base 687A to the femur.

The femur tracker 686A and/or the femur base 687A can include one ormore points 690. The points 690 can include Points A, B, C as describedherein. The femur tracker 686A and/or the femur base 687A can includethree points 690. In the illustrated embodiment, the femur base 687Aincludes one point 690 and the femur tracker 686A includes two points690. Other configurations are contemplated (e.g., one point on the femurbase 687A, two points on the femur base 687A, three points on the femurbase 687A, four points on the femur base 687A, five points on the femurbase 687A; one point on the femur tracker 686A, two points on the femurtracker 686A, three points on the femur tracker 686A, four points on thefemur tracker 686A, five points on the femur tracker 686A, etc.). Thepoints 690 can include divots. The points 690 can include markings. Thefemur tracker 686A and the femur base 687A can be separate components.In other embodiments, the femur tracker 686A and the femur base 687A canbe a unitary structure.

The femur tracker 686A can include a bracket 689A as shown in FIG.27A-27C. In the illustrated embodiment, the bracket 689A can besubstantially vertical in use, as shown in FIG. 25C. The femur tracker686A can include a lock lever 691A. The lock lever 691A can be coupledto the bracket 689A with pivot pins. The lock lever 691A can be pivotedrelative to the bracket 689A. The femur tracker 686A can include anextension 693A. The extension 693A can include the points 690.

The femur base 687A can include a fifth coupler 695A as shown in FIG.28A-28C. The femur tracker 686A can be designed to couple with the fifthcoupler 695A of the femur base 687A. In some embodiments, the taperedsurface of the fifth coupler 695A causes the pivoting of the lock lever691A. In some embodiment, the surgeon causes the pivoting of the locklever 691A. The lock lever 691A can include a detent which is sized andshaped to be received within the slot 697A. The engagement of the detentand the slot 697A can rigidly couple the femur tracker 686A with thefemur base 687A.

FIG. 25B illustrates a parked configuration or home position of theprobe 678A. In some embodiments, a portion of the distal end 680A ismoved into engagement with the platform 620A. In some techniques, thedistal end 680A of the probe 678A engages the divot 630A of the platform620A. At the surgeon's discretion the system 600A can be used tonavigate a condition of the femur prior to hip replacement.

The system 600A can include features that provide notable advantages forthe surgeon. The system 600A can include modular instruments. In someembodiments, the fixation base 602A can include a low profile platform620A. The low profile fixation base 602A can prevent the obstruction ofthe surgical field. The first assembly 604A can be easily removed whennot in use. The distal end 680A of the probe 678A can be angled, bent orcurved to facilitate acquiring one or more landmarks or points. Thedistal end 680A of the probe 678A can be bent or curved to reach thehome position. The femur tracker 686A can be releasably coupled to thefemur base 687A. The femur tracker 686A can be easily removed when notin use. The femur tracker 686A and/or the femur base 687A can providepoints on multiple planes.

5. Posterior Approach: Methods an Orientation Sensing Device and aCamera

FIGS. 18 and 25A illustrate a step of a navigated hip joint implantprocedure discussed in detail below. Some of the preceding steps involveremoving the to-be-replaced joint, navigating the hip joint, preparingthe implant location for the artificial joint, and placing the joint, aselaborated below. As discussed further below, FIGS. 18 and 25Billustrate a technique for confirming that these steps were properlyperformed.

Referring back to FIG. 2, Points A-H are locations on the anatomy thatmay be relevant to various methods and systems herein. In someembodiments, the navigation system 600, 600A is configured to locate arelevant anatomical feature to aid in proper placement of a prosthetichip joint. In some methods, pre-operative imaging techniques are used.In some methods of use, the surgeon can use a standing or supineanteroposterior (AP) pelvic x-ray. FIG. 29 shows standing AP radiographtaken with patient standing with feet in neutral rotation and shoulderwidth apart in stance. The x-ray tube-to-film distance should be 120 cm,with the crosshairs centered on the midpoint between the superior borderof the pubic symphysis and a line drawn connecting the anterior superioriliac spines (ASIS). The coccyx should be centered in line with thepubic symphysis, and the iliac wings, obturator foramina andradiographic teardrops should be symmetrical in appearance. Forappropriate pelvic inclination, a 1-3 cm gap should be seen between thetip of the coccyx and the superior border of the pubic symphysis. Thispositioning can be important for measuring the patient specific RimTeardrop (RT) angle.

To obtain the patient specific Rim Teardrop (RT) angle from the APpelvic x-ray the surgeon can complete one or more of the followingsteps. The surgeon can draw a line on the x-ray connecting the bottom ofthe teardrops. The surgeon can draw a line from the most lateral pointon the rim of the acetabulum (R) on the operative side through thebottom of the teardrop (T) to the horizontal inter-teardrop line. Ifosteophytes are present on the rim (R), the surgeon can draw a linethrough the most lateral osteophyte. The surgeon can measure the anglebetween the inter-teardrop line and the RT line just drawn. This patientspecific RT inclination angle can be an input for the system 600, 600A.

FIG. 30 shows the patient positioning for the posterior hip approach. Inthe posterior hip approach, the patient should be placed in the lateraldecubitus position. When positioning the patient prior to surgery, thesurgeon should take care to align the anterior pelvic landmarks (bothASIS and pubic tubercle) in a vertical plane parallel to the long edgeof the operating table. The surgeon should ensure that the pelvis issecurely held by an appropriate positioning device such as a peg boardor vise-type patient positioner.

The surgical orientation device 172 and the orientation sensing device204 should be turned on. If different programs are present, the surgeonshould select the hip procedure program. If different programs arepresent, the surgeon should select the posterior hip approach. Thesurgeon can verify that patient is positioned in the standard lateraldecubitus position. The surgical orientation device 172 can include adisplay screen. The display screen can confirm the communication betweenthe surgical orientation device 172 and the orientation sensing device204.

The system 600, 600A can be partially assembled for calibration as shownin FIG. 31. The pelvic bracket 638 can be coupled to the extension 644,if separate components. The surgical orientation device 172 can becoupled to the mount 646. In some techniques, the extension 670 can becoupled to the second coupler 648. The orientation sensing device 204can be coupled to the mount 672. The surgical orientation device 172 andthe orientation sensing device 204 form a general V-shapedconfiguration. The orientation sensing device 204 can be fixed inposition relative to the surgical orientation device 172.

The surgical orientation device 172 and the orientation sensing device204 can be calibrated. The assemblies 604, 606 or 604A, 606A can beangled forward so that the backside of the surgical orientation device172 rests on a level surface. The surgeon can hold the assemblies 604,606 or 604A, 606A steady until the surgical orientation device 172indicates completion. The assemblies 604, 606 or 604A, 606A can beangled backward so that the backside of the orientation sensing device204 rests on a level surface. The surgeon can hold the assemblies 604,606 or 604A, 606A steady until the surgical orientation device 172indicates completion. The assemblies 604, 606 or 604A, 606A can beplaced on the left side so that the left side of the surgicalorientation device 172 rests on a level surface. The surgeon can holdthe assemblies 604, 606 or 604A, 606A steady until the surgicalorientation device 172 indicates completion. The assemblies 604, 606 or604A, 606A can be angled forward again so that the backside of thesurgical orientation device 172 rests on a level surface to verifycalibration. The surgeon can hold the assemblies 604, 606 or 604A, 606Asteady until the surgical orientation device 172 indicates completion.In some embodiments, the displayed angles should be less than 2°, lessthan 1°, approximately 0° etc. to verify calibration.

The extension 670 can be decoupled to the second coupler 648. The secondassembly 606, 606A can be assembled as shown in FIGS. 22B and 25A. Themount 658 can be coupled to the probe bracket 652. The mount 658 canrotate relative to the probe bracket 652. The mount 658 can be coupledto the dock 662. The dock 662 can pivot relative to the mount 658 aboutone or more pivot pins 660. The extension 670 can be coupled to thethird coupler 668 of the dock 662. The orientation sensing device 204can be coupled to the mount 672. The probe bracket 652 can be coupled tothe second coupler 648. The first assembly 604, 604A can be coupled tothe second assembly 606, 606A as shown in FIGS. 18 and 25A.

The probe 678 can be inserted within the through lumen 664 of the dock662. The marking 682 can be beneath the camera 684. The surgeon canverify the camera 684 is capturing the measurements of the marking 682by sliding the probe 678 to different positions. The surgicalorientation device 172 can display different positions of the probe 678as the probe 678 is moved. The probe 678A can be similarly positionedwithin the second assembly 606A as shown in FIG. 25A.

The system 600, 600A can be attached to the pelvis. The fixation pins610, 612 can be inserted into the bone. In some techniques, one or moreof the fixation pins 610, 612 are positioned approximately 10 mm abovethe most superior point on the acetabular rim. The fixation pins 610,612 can be perpendicular to the long axis of the patient. The fixationpins 610, 612 can be inserted by use of a driver. In other embodiments,the fixation pins 610, 612 are driven into bone with a mallet until thedistal ends are fully seated within the bone.

The fixation pins 610, 612 can be inserted into the channels 626, 628prior to or after the fixation pins 610, 612 are driven into the bone.The support 622 can be brought toward the platform 620, therebydecreasing the diameter of the channels 626, 628. The fixation pins 610,612 can be secured to the fixation base 602. The first assembly 604 canbe coupled to the first coupler 632. The surgical orientation device 172can be coupled to the first assembly 604. The second assembly 606 can becoupled to the second coupler 648. The orientation sensing device 204can be coupled to the second assembly 606. The system 600 can bepositioned as shown in FIG. 18. The fixation base 202A can be affixedwith fasteners 613A, as shown in FIG. 25B. The system 600A can bepositioned as shown in FIG. 25B.

The femur tracker 686, 686A can be coupled to the femur. The femurtracker 686 can be positioned on the greater trochanter. The curved endof the femur tracker 686 can be pointing toward the head of the patient.One or more fixation devices can be placed through the each hole 688 ofthe femur tracker 686 to secure the femur tracker 686 to the femur. Thefemur tracker 686 can be positioned as shown in FIG. 18. The femur base687A can be positioned on the greater trochanter. The femur tracker 686Acan be assembled as shown in FIG. 25C. The femur tracker 686A can becoupled to the femur base 687A as described herein.

If different programs are present, the surgeon should select which hipis being operated on (e.g., right or left hip). The surgeon can verifythat patient is positioned in the standard lateral decubitus position.If different programs are present, the surgeon should select the genderof the patient being operated on (e.g., male or female). If differentprograms are present, the surgeon should select the target cupinclination angle. This angle can be selected based upon theradiographic inclination angle. If different programs are present, thesurgeon should select the target cup anteversion angle. This angle canbe selected based upon the radiographic anteversion angle. If differentprograms are present, the surgeon should select the RT inclinationangle. This angle can be selected based upon the radiographic RTinclination angle, such as from the A/P pelvic x-ray.

The surgeon can register a parked configuration or home position. Insome techniques, the distal end 680, 680A of the probe 678, 678A can beengaged with a point on the platform 620, 620A. The platform 620, 620Acan include the divot 630, 630A. The divot 630, 630A can be sized toaccept the distal end 680, 680A of the probe 678, 678A. This position isshown in FIGS. 18 and 25B. The probe 678, 678A can be angled relative tovertical in the home position. The dock 662 can be angled relative tovertical in the home position. The orientation sensing device 204coupled to the dock 662 can be angled relative to vertical in the homeposition. The surgical orientation device 172 can be also angledrelative to vertical in the home position.

The orientation sensing device 204 can register the operating table, inother words perform table registration. The patient can be positioned sothat the sagittal plane of the pelvis is level. The surgeon can alignthe probe 678, 678A with the horizontal. The probe 678, 678A can beparallel with the coronal plane. The system 600, 600A can calculate cupangles based on the assumption that the pelvis of the patient iscorrectly positioned during table registration.

The femur can be positioned in a neutral reference position with respectto flexion, abduction and rotation. This neutral position can berepresentative of a standing position of the patient. The femur shouldbe maintained in this position during the initial registration of points690, such as Points A, B, and C, shown in FIGS. 24A and 25C. The surgeoncan confirm that the orientation sensing device 204 is coupled to thedock 662. The surgeon can position the distal end 680, 680A of the probeat Point A of points 690. In some methods, the distal end 680, 680A isplace within a divot at Point A on the femur tracker 686, femur base687A. The surgeon can enter an input to register Point A (e.g., depressa button on surgical orientation device 172). The surgical orientationdevice 172 can indicate that Point A was recorded. The surgeon canposition the distal end 680, 680A of the probe at Point B of points 690.In some methods, the distal end 680, 680A is place within a divot atPoint B on the femur tracker 686, 686A. The surgeon can enter an inputto register Point B (e.g., depress a button on surgical orientationdevice 172). The surgical orientation device 172 can indicate that PointB was recorded. The surgeon can position the distal end 680, 680A of theprobe at Point C of points 690. In some methods, the distal end 680,680A is place within a divot at Point C on the femur tracker 686, 686A.The surgeon can enter an input to register Point C (e.g., depress abutton on surgical orientation device 172). The surgical orientationdevice 172 can indicate that Point C was recorded.

The surgeon can position the distal end 680, 680A of the probe 678, 678Aat various anatomical landmarks. FIG. 32 illustrates four landmarkswhich can be utilized in some techniques. In one technique, Point 1 isthe most superior point of rim. The surgeon should not remove anyosteophytes from this landmark prior to registration of Point 1. Point 1registered landmark should match the anatomy identified on thepre-operative x-ray. In some methods, the distal end 680, 680A of theprobe 678, 678A is placed at Point 1. The surgeon can enter an input toregister Point 1 (e.g., depress a button on surgical orientation device172). The surgical orientation device 172 can indicate that Point 1 wasrecorded.

Point 2 can be the most inferior point of the acetabular notch. Thesurgeon should not remove any osteophytes from this landmark prior toregistration of Point 2. Point 2 registered landmark should match theanatomy identified on the pre-operative x-ray. The transverse acetabularligament (TAL) straddles the inferior limit of the bony acetabulum. Itis a strong load-bearing structure and, in the normal hip, inassociation with the labrum, provides part of the load-bearing surfacefor the femoral head. In some methods, the distal end 680, 680A of theprobe 678, 678A is placed at Point 2. The surgeon can enter an input toregister Point 2 (e.g., depress a button on surgical orientation device172). The surgical orientation device 172 can indicate that Point 2 wasrecorded.

Point 3 can be the posterior insertion of the transverse acetabularligament (TAL). The surgeon should remove any osteophytes from thislandmark prior to registration of Point 3. This will uncover orreplicate native anatomy of the landmark. In some methods, the distalend 680, 680A of the probe 678, 678A is placed at Point 3. The surgeoncan enter an input to register Point 3 (e.g., depress a button onsurgical orientation device 172). The surgical orientation device 172can indicate that Point 3 was recorded.

Point 4 is the anterior insertion of the transverse acetabular ligament(TAL) in one embodiment. The surgeon should remove any osteophytes fromthis landmark prior to registration of Point 4. This will uncover orreplicate native anatomy of the landmark. In some methods, the distalend 680, 680A of the probe 678, 678A is placed at Point 4. The surgeoncan enter an input to register Point 4 (e.g., depress a button onsurgical orientation device 172). The surgical orientation device 172can indicate that Point 4 was recorded.

When registering the anatomical points or points 690 on the femurtracker 686, the camera 684 captures an image of the marking 682. Thecamera 684 can read the marking 682 to provide accurate determination ofthe translational position of the probe 678 relative to the dock 662.The camera 684 can be directly above the marking 682. In some methods,the camera 684 can read a binary code of the marking 682.

In some methods, the orientation sensing device 204 converts the imageof the camera 684 into an extension measurement of the probe 678. Insome embodiments, the surgical orientation device 172 converts the imageof the camera 684 into an extension measurement of the probe 678. Thedistance related to the extension of the probe 678 can be used inconjunction with the orientation and positional data from theorientation sensing device 204. The surgical orientation device 172 canuse the length measurement from the camera 684 and the data from theorientation sensing device 204 to determine the location of the distalend 680 of the probe 678. In some embodiments, the surgeon will enter aninput (e.g., depress a button) to collect data from the orientationsensing device 204. In some methods, the surgeon will enter an input(e.g., depress a button) to collect data from the camera 684. In someembodiments, the surgeon will enter an input (e.g., depress a button) tocollect data from the orientation sensing device 204 and the camera 684simultaneously. In some methods, the orientation sensing device 204and/or the camera 684 will only send data to the surgical orientationdevice 172 if the orientation sensing device 204 is stable ornon-moving. The points 690 can include divots to stabilize the distalend 680, 680A of the probe 678, 678A when the points 690 are registered.

The surgeon can set the angle of the cup. Later in the procedure, thesurgeon can check cup angle after the angle has been set. The surgeoncan remove the second assembly 606, 606A from the first assembly 604,604A. The surgeon can remove the extension 670 from the third coupler668. The surgeon can couple the extension 670 to an impactor 300B, shownin FIGS. 56A-56F. The impactor 300B can have a fourth coupler 338B. Insome embodiments, the fourth coupler 338B is a universal coupler. Insome embodiments, the fourth coupler 338B is identical or substantiallysimilar to the second coupler 648 and the third coupler 668. Thispermits the orientation sensing device 204 to couple to either thesecond coupler 648, the third coupler 668 or the fourth coupler 338B, asdescribed herein The fourth coupler 338B can be similar to the firstcoupler 632 described herein. The fourth coupler 338B can extend from aside surface of the impactor 300B. The fourth coupler 338B can extendperpendicularly to the longitudinal axis of the impactor 300B. Theextension 670 can couple to the fourth coupler 338B. The mount 672 canbe coupled to the orientation sensing device 204. The acetabular shellcan be threaded onto the shell adaptor, similar to FIG. 11C. The shelladaptor can be snapped onto the end of the impactor 300B, similar toFIG. 11B.

The acetabular shell can be inserted into the acetabulum and positionedat the desired angle. The surgical orientation device 172 can guide thesurgeon in setting the appropriate cup angle. The surgical orientationdevice 172 can graphically display when the orientation sensing device204 is located at the inclination and anterversion angles enteredpreviously. The surgical orientation device 172 can graphically displaythe inclination and anterversion angles as the orientation sensingdevice 204 is moved. The surgeon can enter an input to set the desiredangle (e.g., depress a button on surgical orientation device 172). Thesurgical orientation device 172 can output all inclination andanteversion angles according to radiographic definitions. Anteversion(Radiographic Anteversion) is the angle between the acetabular axis andthe coronal plane. Inclination (Radiographic Inclination) is the coronalplane projection of the angle between the acetabular axis and thelongitudinal axis of the body. Once the orientation sensing device 204is coupled to the impactor 300B, the surgical orientation device 172 candisplay the radiographic inclination and anteversion angles of theimpactor 300B relative to the frontal pelvic plane.

The inclination and anteversion cup angles can be displayed statically.The inclination and anteversion cup angles can be displayed statically.The anatomic angles are those calculated by the system 600 based on thepelvic landmark registration. The table angles are those calculated bythe system 600 based on the initial positioning of the pelvis duringtable registration. In some embodiments, the orientation sensing device204 can register the operating table by aligning the probe 678, 678Awith the horizontal. In some embodiments, only the direction of theprojection of the probe 678, 678A onto a horizontal plane is used. Theprobe 678, 678A can be in an infinite number of angles from horizontal,which would result in the same software result. This is convenient dueto the mechanical constraints imposed by the pivot configuration of thesystem 600. The angles displayed can be an average between the anatomicreference and table reference. The inclination angle is calculated basedas an average between the anatomic reference and table reference. Theanteversion angle is calculated based on the table reference. Thesurgeon can check cup angle after the angles are set.

The surgeon can register the hip center. The surgeon can couple thesecond assembly 606, 606A to the first assembly 604, 604A as shown inFIGS. 18 and 25A. The mount 672 can be coupled to the orientationsensing device 204. The mount 646 can be coupled to the surgicalorientation device 172. The surgeon can confirm that the components ofsystem 600, 600A are rigidly coupled. The surgeon can select the firstset of points on the rim of the shell 360 to be registered, as shown inFIG. 33. In the illustrated method, the first set of points is selectedon the rim of the shell. The surgeon can place the distal end 680, 680Aof the probe 678, 678A on each of the first set of points shown in FIG.33. In some methods, the surgeon can select the second set of points onthe rim of the shell to be registered. In the illustrated method, thesecond set of points is selected on the rim of the shell. The surgeoncan place the distal end 680, 680A of the probe 678, 678A on each of thesecond set of points. In some methods, the surgeon should select thethird set of points on the rim of the shell to be registered. In theillustrated method, the third set of points is selected on the rim ofthe shell. The surgeon should place the distal end 680, 680A of theprobe 678, 678A on each of the third set of points. In some methods, theminimum separation distance allowed between points is 25 mm. In somemethods, the maximum separation distance allowed between points is 65mm.

The inclination and anteversion angles of the shell are displayed on thesurgical orientation device 172. These angles are based on the planedetermined by the three points registered on the rim. The surgeon canenter the offset of the liner to be used. The offset is the distancefrom the center of the shell face to the center of the femoral head. Ifthe shell is hemispherical and the head and shell are concentric, thesurgeon can enter zero. In some methods, the offset is between 0 mm and10 mm. The surgeon can repeat this step if the linear offset is changedlater in the procedure. The surgical orientation device 172 cancalculate the center of rotation (COR) of the hip using the set ofpoints on the rim of the shell.

The surgeon can register the leg length and offset after implantation ofthe acetabular shell. The surgeon can couple the second assembly 606,606A to the first assembly 604, 604A as shown in FIGS. 18 and 25A. Themount 672 can be coupled to the orientation sensing device 204. Themount 646 can be coupled to the surgical orientation device 172. Thesurgeon can confirm that the components of system 600, 600A are rigidlycoupled. The femur can be repositioned within +/−20° flexion from thepre-operative position. The femur can be repositioned within +/−15°abduction from the pre-operative position. The femur can be repositionedwithin +/−20° rotation from the pre-operative position.

In some methods, the distal end 680, 680A of the probe 678, 678A isplace within a divot at Point A of points 690. The surgeon can enter aninput to register Point A (e.g., depress a button on surgicalorientation device 172). The surgeon can position the distal end 680,680A of the probe at Point B of points 690. The surgeon can enter aninput to register Point B (e.g., depress a button on surgicalorientation device 172). The surgeon can position the distal end 680,680A of the probe at Point C of points 690. The surgeon can enter aninput to register Point C (e.g., depress a button on surgicalorientation device 172). The surgical orientation device 172 canindicate that Points A, B, and C were recorded. Using Points A, B, andC, the surgical orientation device 172 can calculate the change in anglebetween the pelvis and the femur since the initial registration prior todislocation. The surgical orientation device 172 can mathematicallyrotate the femoral points, Points A, B, and C, around the center ofrotation (COR) of the hip to align the femur with its initial position.The new position of the centroid of the femoral points, Points A, B, andC, is compared to the initial position. The femoral points, Points A, B,and C, can be located on the femur tracker 686, 686A or femur base 687.

The leg length and offset are displayed on the surgical orientationdevice 172. The change in leg length is in the proximal distaldirection. The joint offset is in the medial lateral direction. If theangle between the femur and the pelvis has changed by more than a hardcoded limit in any axis, then the surgical orientation device 172 candisplay an error message. The hard coded limit can be 15°, between10-20°, between 5-25°, etc. The surgical orientation device 172 candisplay guidance on repositioning the femur (e.g., abduct femur, flexfemur, etc.). The surgeon can exchange or reposition the shell to adjustleg length and offset. The surgeon can exchange or reposition the shellbased upon goals from pre-operative templates or images. If desired andpossible, the leg length and offset may be adjusted according to thesurgeon's standard surgical procedure.

The surgeon can register the home position. The surgeon can couple thesecond assembly 606, 606A to the first assembly 604, 604A as shown inFIGS. 18 and 25A. The mount 672 can be coupled to the orientationsensing device 204. The mount 646 can be coupled to the surgicalorientation device 172. The surgeon can confirm that the components ofsystem 600, 600A are rigidly coupled. The surgeon can verify the parkedconfiguration or home position. The distal end 680, 680A of the probe678, 678A can be engaged with a point on the platform 620, 620A. Theplatform 620, 620A can include the divot 630, 630A. The divot 630, 630Acan be sized to accept the distal end 680, 680A of the probe 678, 678A.This position is shown in FIGS. 18 and 25B. The change in the homeposition is displayed on the surgical orientation device 172. The numbermay not be zero due to mechanical play and/or sensor noise. If thedisplayed number is greater than 3 mm, the surgeon may wish to verifythe rigid connection between the components of the system 600, 600A.

B. Navigation Using Inertial Sensors and Jigs for Referencing AnatomicalLandmarks with Anterior Approach

1. Anterior Approach: Systems with an Orientation Sensing Device Coupledto a Probe

FIGS. 34-38 illustrate a hip navigation system 500 adapted to navigate ahip joint procedure from an anterior approach. Anterior approach to hipreplacement advantageously can be less invasive than posterior approach.In particular, the anterior approach can enable smaller incisions, lesssoft tissue dissection, and shorten recovery time for patients. Thesystem 500 includes an anchor system 504, an alignment assembly 508 anda landmark acquisition assembly 512.

FIG. 34 shows the anchor system 504 in more detail. The system 504 isconfigured to securely couple the navigation system 500 to the hip, suchthat movement between the system and the hip are minimized oreliminated. The anchor system 504 includes a cannula 516 having a distalend 520 and a proximal end 524 with a lumen 532 extending between thedistal and proximal ends. The proximal end 524 of the cannula 516 iscoupled with a platform 536, for example adjacent to one lateral end ofthe platform. The platform 536 is similar to those hereinbeforedescribed having a plurality of docking device 538, 538A disposed awayfrom the location where the proximal end 524 and the platform 536 areconnected.

The docking devices 538 are configured to couple with detachablemounting devices that securely but temporarily couple sensor to theanchor system 504. The two docking device 538 on the top surface of theplatform 536 enable the anchor system 504 to be used for either left orright hip procedures. As shown in FIG. 34, the docking device 538 on theside of the platform 536 closest to the medial plane of the patient ispreferably used for docking. The top side docking feature not in use inFIG. 34 would in fact be used in performing a procedure from the otherside of the patient. The docking device 538A on the side surface of theplatform 536 is provided for a temporary intra-procedure mounting of asensor to the platform 536. As discussed further below, this temporarymounting provides a known orientation and/or location of two sensorsrelative to each other during a procedure, which enables the system 500to control sources of error with certain types of sensors.

The platform 536 also can have a channel 540 disposed away from thecannula 516. The channel 540 can have a lumen disposed along an axissubstantially parallel to the lumen 532 of the cannula 516. In oneembodiment, the anchor system 504 is configured to securely couple theplatform 536 to the hip by placement of two spaced apart pins 544A,544B. FIG. 34 shows that the pin 544A can be advanced through thecannula 516 such that a distal end of the pin 544A contacts andpenetrates a bony prominence of the pelvis. In one technique the pin544A is positioned at or as close as possible to the anterior superioriliac spine (ASIS) of the pelvis. The pin 544B is advanced through thechannel 540 and into the pelvis at a location offset form the ASIS. Thedistance between the pins 544A, 544B and the precise positioning of thepin 544B are not critical, but are determined by the locations of theconnection of the cannula 520 to the platform 536 and of the channel540.

The pins 544A, 544B can take any suitable form but preferably have thesame cross-sectional profile as the lumens in the cannula 520 and in thechannel 540, e.g., they can be circular in cross-section. The pins 544A,544B can be modified Stienmann pins, e.g., configured to extend at leastabout 5 cm above the platform 536 and having a diameter of about 4 mm.

The anchor system 504 also has a locking device 556 for securing theplatform 536 to the pins 544A, 544B. In one embodiment, the portion ofthe platform disposed around the pins comprises medial and lateralportions 560M, 560L that can move away from each other to release thepins 544A, 544B or toward each other to frictionally engage the pins.For example, a pair of hex-driven screws can engage the medial andlateral portion 560M, 560L to translate them toward and away from eachother respectively. The locking device 556 preferably is quickly andeasily removed from the pins such that other instrument, such as X-Rayor other diagnostic devices can be brought into the vicinity of thesurgical field during the procedure. Preferably the pins 544A, 544B havemarkings along their length such that if the platform 536 is removed forimaging or other reasons it can be quickly re-positioned at the sameelevation.

The cannula 520 also has a foot 568 adjacent to or at the distal end 528to minimize or eliminate error that could arise due to unevenpenetration depth of the anchor system 504 when compared to the positionof a distal probe of the landmark acquisition system 512 when landmarksare being acquired. The foot 568 can include an annular projectiondisposed outward of the cannula 520. Preferably the foot 568 extendslaterally from the outer surface of the cannula 520 by a distance equalto or greater than the wall thickness of the cannula 520. In someembodiment, the surface area beneath the foot is equal to or grater thanthe surface area of the cannula when viewed in cross-section at alocation where the foot 568 is not located, e.g., at an elevation aboutthe foot 568.

The alignment assembly 508 is similar to those hereinbefore described.It can have a rigid extension 570 configured to detachably secure aorientation device 172 to the docking device 538.

The landmark acquisition assembly 512 is similar to those hereinbeforedescribed, but is configured to be unobstructed in use by soft tissueanterior to the pelvis of the patient. In one embodiment, an extension578 is provided to elevate a pivoting and sliding mechanism 582. Thepivoting and sliding mechanism enables a probe arm 584 to slide awayfrom the extension 578 toward the location of landmarks to be acquired.The pivoting and sliding mechanism 582 can be similar to any of thosediscussed above. The distal (lower) end of the extension 578 can becoupled to the platform 536 in any suitable way. For example, the distalend can include a pin-like projection that is received in, e.g.,friction fit in, an aperture 578A having the same shape. Detents orother locking features can be provided to securely connect the extensionto the platform 536 in the aperture 578A. FIG. 35 shows that theaperture 578A can be formed in a portion of the platform 536 that iselevated compared to the portions of the platform through which the pin544A extends. This portion is elevated to provide sufficient bearingengagement to minimize play. It also has a slot generally parallel tothe top surface of the platform 536 which serve the function of engaginga ball detent on the lower end of the extension 578.

The probe arm 584 can be configured as an elongate member with aplurality of markings, discussed below. A distal end of the probe arm584 can include an angled tip 586 that assists in probing anatomy insome techniques, e.g., portions of the femur for leg length and femoralhead positioning confirmation. In the posterior approach, the angled tip586 is used to directly contact anatomy.

In the anterior approach, the angled tip 586 is coupled with a probeextension 590 configured to contact selected anatomy. The probeextension 590 has an upright member 592 that is configured to extend, inthe anterior approach, between the elevation of the probe 584 downtoward the elevation of the tissue to be probed. A foot 594 on thedistal (lower) end of the upright member 592 is configured to engage thetissue in a way that minimizes error due to uneven tissue compressionbetween the point of mounting of the pin 544A and the foot 594. Forexample, the foot 594 can have a cross configuration that spreads outthe force or pressure applied by the landmark acquisition system 512 inuse. The proximal end of the extension 590 includes a coupler 596 thatconnects a distal end of the probe arm 584 with the upright member 592.Preferably the coupler 596 is easily manipulable by the user to modifyconnect to the probe arm 584. The coupler can include an L-shaped memberwith an aperture configured to receive the tip 586 of the probe arm 584.A set screw can be advanced through the L-shaped portion to lock the arm584 in place. The L-shaped portion is configured to couple to the arm584 such that the tip of the angled tip 586 rests on a projection of thelongitudinal axis of the upright member 592.

2. Anterior Approach: Methods with an Orientation Sensing Device Coupledto a Probe

The system 500 can be used to navigate from an anterior approach in thefollowing ways. The orientation device 172 and the sensor 204 can bepaired such that they are in wireless communication with each other.This permits one or other of the device 172 and sensor 204 to controlthe other, store data from the other, and/or display information basedon signals from the other. In one method, the orientation device 172 hasa display that confirms to the surgeons certain angles based on the datasensed by the sensor 204. The pairing the device and sensor 172, 204 caninvolve coupling them together and comparing sensor output between thetwo devices at a plurality of orientations, e.g., horizontal, vertical,and angled at 30 degrees. Some of these positions may be repeated with aplurality of attitudes, e.g., vertical with left side up, vertical withright side up, and vertical with top side up.

As noted above, the components discussed herein can be provided as a kitthat enables the surgeon to select among different surgical approaches,e.g., posterior and anterior approaches. The orientation device 172 andsensor 204 may operate differently in these different approaches. Thus,in one method the user will enter into one or both of the orientationdevice and sensor 172, 204 which approach is being used. This willimplement a software module in the orientation device 172 (or in thesensor 204 is the processor running the software is located there)corresponding to the selected approach.

In various embodiments suitable for the anterior approach, theorientation device 172 and the sensor 204 can both have a plurality ofsourceless sensors. These components can have both accelerometers andgyroscopes in some embodiments. Some gyroscopes are subject toaccumulated error that can be significant in the time frames relevant tothese methods. Accordingly, various methods are provided to prevent sucherrors from affecting the accuracy and reliability of the anglesdisplayed to the surgeon by the system 500. Some approaches can beperformed with accelerometers only. For example, variations of theanterior approach can be performed with accelerometers with somewhatless but still acceptable accuracy using accelerometers only. Thereduction in accuracy of the accelerometers is balanced against thebenefit of eliminating the accumulated error that arises with somegyroscopes. The resolution of accelerometers is sufficient because thepoints navigated are relatively far apart.

The calculations performed by the system 500 are unique to the hip beingtreated in some embodiment, so the system receives input of the hipbeing treated.

The foot 568 is placed on a selected anatomical location, e.g., on theASIS as discussed above. With the cannula 520 in an approximatelyvertical orientation the platform 536 is secured to the hip. Securingthe platform 536 to the hip can be done in any suitable way, such aswith two spaced apart Stienmann pins. Thereafter, the orientation device172 and the sensor 204 are attached to the platform 536 in the mannershown in FIG. 36A. Depending on the nature of the sensing devicesdeployed in the sensor 204 it may be advantageous to initialize thesensor at this point of the procedure. As discussed above, certaininertial sensors (e.g., some gyroscopes) are subject to accumulatederror. One technique for managing this error source is to periodicallyinitialize or zero out this error. Some techniques involve initialing atthis point.

In some embodiment, a frame of reference based on the plane of the tablecan be input into the system 500. The table reference frame can be asecondary reference frame. In one technique, the sensor 204 is movedfrom the platform dock position of FIG. 36A to the navigating positionon the probe arm 584 as shown in FIG. 34. The probe arm 584 is thenpivoted by the mechanism 582 such that the arm points in a directionthat is parallel to the patient's medial-lateral mid-plane and theangled tip 586 superiorly (generally toward the patient's head). Theprobe arm 584 is also held substantially parallel to the plane of thetable. With this heading and orientation the user interacts with a userinterface on the orientation device 172 to signal to the orientationsystem 508 to capture the orientation of the sensor 204. Thisorientation provides an estimation of the orientation of the anteriorpelvic plane. This estimation may be tracked in the system 500 and mayalone provide an improvement over the state of the art in un-navigatedhip replacement, which involves discrete maneuvers guided by the unaidedeye.

At the surgeon's discretion the system 500 can be used to navigate acondition of the femur prior to hip replacement. A mark Fm may be madeon the proximal femur. Thereafter the sensor 204 can be initialized orzeroed such as by placing it back in the dock position on the platform(as in FIG. 36A). Thereafter, the probe tip 586 can be brought intocontact with the femur mark Fm and locked in place in such contact. SeeFIG. 37. The sensor 204 can be transferred to the proximal end of theprobe 584 and the orientation device 172 can be signaled to record theorientation of the sensor 204. A distance from the point of attachmentof the cannula 520 to the ASIS to the marked position on the femur canthen be recorded in the orientation device 172. The position can bebased on reading graduated marks on the probe 584 or can be capturedautomatically by a camera system or a sensor built into the system 500.In one embodiment, graduated marks are read at an upright edge 598within a bight of a sliding portion of the pivoting and slidingmechanism 582.

FIG. 36A illustrates a further step of navigating the anterior pelvicplane. As shown, the sensor 204 is docked on the platform 536, in whichposition any accumulated error associated with some sensors can beeliminated. In a preceding step, the extension 590 is coupled with thedistal portion of the probe 584. The foot 594 is brought into contactwith the contralateral ASIS. Thereafter, the sensor 204 can be attachedto the proximal end of the probe 284 as shown in FIG. 34. The landmarkacquisition system 512 can be immobilized and the orientation of thesensor 204 can be recorded in memory in the orientation device 172.Additionally, the distance that the probe 584 is extended to contact thecontralateral ASIS can be recorded in the orientation device 172. Asnoted above, that distance can be read from the scale on the probe 584at the upright edge 598.

The process to record the contralateral ASIS can be repeated for one ormore additional points. The sensor 204 can be docked to the platform asin FIG. 36A to eliminate sources of accumulated error. The probe 584 canthen be moved to cause the foot 594 to be in contact with a pubictubercle. The probe 584 can be immobilized and the sensor coupled withthe proximal end as shown in FIG. 36B. Thereafter data indicative of theorientation of the sensor 204 and the distance to the pubic tubercle arerecorded in the orientation device 172 in any of the manners discussedabove.

Once the foregoing points of the pelvis have been navigated and the datarecorded into the orientation device 172 the anterior pelvic plane canbe calculated from data indicating the navigated points. The orientationof the anterior pelvic plane is a baseline for placement of the cupportion of a hip prosthesis.

The sensor 204 and the orientation device 172 can at this point be usedto guide placement of the cup 360 in the prescribed orientation. Priorto placement the impactor 300, 300A is provided. For example, theimpactor 300A can be provided by selecting the appropriate tip component348 onto the distal end of the shaft 316A. The tip component 348 iscoupled with the cup 360, e.g., by threads. The rotational orientationof the cup 360 to the shaft 316A that is most convenient given holepatterns and position of the sensor 204 is selected by matching up theflats 350A, 350B as appropriate. During the process of providing theimpactor 300 the sensor 204 can be docked to the platform 536 and sourceof accumulated error can be eliminated just prior to navigating the cup360 into place in the acetabulum.

In one technique, the cup 360 is inserted into the acetabulum and placedto approximately the correct orientation. Thereafter the sensor 204 isconnected to a docking device 338 on the impactor as shown in FIG. 11A.The orientation device 172 is the activated to display angles indicativeof the orientation of the cup, e.g., degrees of inclination andanteversion with respect to the anterior pelvic plane. The angledisplayed can directly reflect the table reference frame discussedabove. The angle displayed can directly reflect the frame of referencefrom the acquisition of landmarks. In some cases, angles can bedisplayed that directly reflect both table reference frame and landmarkreference frame. In other embodiments, the table reference frame is notdisplayed but rather causes a user instruction to be displayed on theorientation device 172, such as a direction to re-acquire landmarks dueto disagreement between the angles generated by the two referenceframes.

Any of the foregoing combinations of table and landmark reference framesprovides redundancy that ensures that the angle information provided tothe user is accurate and reliable such that the procedures performedwill be better contained within the “safe zone”.

When the correct angles are achieved, a tool is used to strike theproximal end of the impactor 300 to lodge the cup 360 in place at thedesired angle. In some techniques, the sensor 204 is removed prior tostriking the proximal end of the impactor 300. The system 500 includes amodule that monitors signals from the sensor 204 and if a largedeviation in the readings occurs, the module prevents the angles on thedisplay of the orientation device from changing. This “freezing” of thedisplay is both a safety and an accuracy precaution because a largeforce due to impact can affect the accuracy of the sensor 204.

If femoral landmarks are acquired in the procedure prior to separatingthe natural joint, the same landmarks can be acquired after theprosthetic joint is placed to confirm that the replacement of the jointhas not changed either the length of the leg, the off-set of the legfrom the trunk of the patient or both. For example, the sensor 204 canbe docked to the docking device 538A as shown in FIG. 36A. Sources ofaccumulated error can be eliminated by initializing the sensor 204.Thereafter, the probe arm 538 can be brought into contact with the samelandmark (e.g., Fm) acquired early in the procedure. See FIG. 38. Theprobe arm 538 can be locked into place and thereafter the sensor 204 canbe coupled with the proximal end of the probe arm 538. The orientationof the sensor and the distance to the probe arm 538 can be input intothe orientation device 172. These data enable the orientation device 172to output amounts of change in leg length and leg offset.

In one variation a plurality of points, e.g., three points, on the femurare acquired before and after the joint is replaced. This approachenables a further confirmation that the rotation orientation of the neckof the femur relative to an axis extending through the center of the cup360 perpendicular to the plane of the acetabulum is unchanged after theprocedure.

Of course, the femur registration procedures enable correction ofdiagnosed deformities including excessive leg length offset and jointoffset, as well as mal-orientation of the femoral neck in the naturaljoint. In other words, the surgeon can begin the procedure with theintent of adding some offset or changing rotational orientation toimprove the patient's bone positions and/or orientationspost-operatively.

3. Anterior Approach: Systems with an Orientation Sensing Device andCamera

FIG. 39 shows the system 600 adapted to navigate a hip joint procedurewith reference to anatomical landmarks from an anterior approach. Thesystem 600 can include the orientation sensing device 204, not shown inFIG. 39, as described above The system 600 can be adapted for either aposterior approach as described above, or an anterior approach.

FIG. 40-42 shows a hip navigation system 600B adapted to navigate a hipjoint procedure with reference to anatomical landmarks from an anteriorapproach. As noted above, in the anterior approach, the patient is inthe supine position. The system 600B can include any of the featuresdescribed above, including with reference to system 600. The system 600Bcan be used in any technique or method step described herein. The system600B can include the surgical orientation device 172 described herein.The system 600B can include the orientation sensing device 204 describedherein. The system 600B can include a camera 684 described herein.

The surgical orientation device 172 and the orientation sensing device204 can be turned on before the procedure begins. If the system can beused in a posterior or anterior approach, one method can involve asurgeon selecting a module corresponding to the approach. For example,the surgeon can select an anterior hip approach module or a posteriorhip approach module in the surgical orientation device 172. In someembodiments, the method can involve the step of inputting the surgicaltechnique into the surgical orientation device 172. The surgeon canverify that patient is positioned in an appropriate position, e.g., in asupine position. The surgical orientation device 172 can include adisplay screen. The display screen can confirm the communication betweenthe surgical orientation device 172 and the orientation sensing device204.

The system 600, 600B can be partially assembled for calibration. In someembodiments, the first assembly 604 can be assembled. The pelvic bracket638 can be coupled to the extension 644, if separate components. Thesurgical orientation device 172 can be coupled to the mount 646. In sometechniques, the extension 670 can be coupled to the second coupler 648.The orientation sensing device 204 can be coupled to the mount 672. Thesurgical orientation device 172 and the orientation sensing device 204form a general V-shaped configuration, similar to the orientation shownin FIG. 31. The orientation sensing device 204 can be fixed in positionrelative to the surgical orientation device 172.

The surgical orientation device 172 and the orientation sensing device204 can be calibrated. The surgical orientation device 172 can be restedon a level horizontal surface with the display pointed upward. Thesurgeon can hold the assemblies 604, 606 or 604B, 606B steady until thesurgical orientation device 172 indicates completion. The surgicalorientation device 172 can be rested on a level vertical surface withthe display pointed sideways. The surgeon can hold the assemblies 604,606 or 604B, 606B steady until the surgical orientation device 172indicates completion. The assemblies 604, 606 or 604B, 606B can beplaced on the left side so that the left side of the surgicalorientation device 172 rests on a level surface. The surgeon can holdthe assemblies 604, 606 or 604B, 606B steady until the surgicalorientation device 172 indicates completion. The assemblies 604, 606 or604B, 606B can be angled forward to verify calibration. The surgeon canhold the assemblies 604, 606 or 604B, 606B steady until the surgicalorientation device 172 indicates completion.

The extension 670 can be decoupled from the second coupler 648, asdescribed herein. The second assembly 606 can be assembled as shown inFIGS. 39 and 40. The first assembly 604, 604B can be coupled to thesecond assembly 606, 606B as shown in FIGS. 39 and 40. The probe 678,678B can be inserted within the through lumen of the dock 662, 662B. Themarking 682 can be beneath the camera 684. The surgeon can verify thecamera 684 is capturing the measurements of the marking 682 by slidingthe probe 678, 678B to different positions. An error message can bedisplayed if the camera 684 is not reading the markings 682.

The system 600, 600B can be attached to the pelvis. The fixation pins610, 612 can be inserted into the bone. In some techniques, one or moreof the fixation pins 610, 612 are positioned over the ASIS on theoperative side. In some techniques, one or more of the fixation pins610, 612 are positioned on the iliac crest. The fixation pins 610, 612can be approximately vertical. The fixation pins 610, 612 can beinserted by use of a driver. The fixation base 602, 602B can be rotatedas needed to place the fixation pins 610, 612 within the channels 626,628 as shown in FIG. 20C. The support 622 can be brought toward theplatform 620, thereby decreasing the diameter of the channels 626, 628.The fixation pins 610, 612 can be secured to the fixation base 602,612B.

The first assembly 604, 604B can be coupled to the first coupler 632 asdescribed herein. The surgical orientation device 172 can be coupled tothe first assembly 604, 604B. The second assembly 606, 606B can becoupled to the second coupler 648 as described herein. The orientationsensing device 204 can be coupled to the second assembly 606. The system600 can be positioned as shown in FIGS. 39 and 41.

The surgeon can register a parked configuration or home position asshown in FIG. 41. In some techniques, the distal end 680, 680B of theprobe 678, 678B can be engaged with a point on the platform 620 orcannula 621B. The platform 620 or cannula 621B can include the divot 630as described herein. The divot 630 can be sized to accept the distal end680, 680B of the probe 678, 678B. The distal end 680, 680B of the probe678, 678B can be curved or bent to facilitate locating anatomicallandmarks or points, as shown in FIGS. 39 and 40. The probe 678, 678Bcan be vertical in the home position. The orientation sensing device 204can be vertical in the home position.

The orientation sensing device 204 can register the operating table orperform table registration for the anterior approach. The patient can bepositioned so that the coronal plane of the pelvis is level. In someembodiments, the surgeon can align the probe 678, 678B with thehorizontal. In some embodiments, only the direction of the probe's 678,678A projection onto a horizontal plane is used. The probe 678, 678A canbe in an infinite number of angles from horizontal, which would resultin the same software result. This is convenient due to the mechanicalconstraints imposed by the pivot configuration of the system 600. Theprobe 678, 678B can be parallel with the sagittal plane. The system 600,600B can calculate cup angles based on the assumption that the pelvis ofthe patient is correctly positioned during table registration.

At the surgeon's discretion the system 600, 600B can be used to navigatea condition of the femur prior to hip replacement. A mark Fm may be madeon the proximal femur. Thereafter the orientation sensing device 204 canbe initialized or zeroed such as by placing it back in the homeposition, as described herein. Thereafter, the distal end 680, 680B ofthe probe 678, 678B can be brought into contact with the femur mark Fm.The surgical orientation device 172 can be signaled to record theorientation of the orientation sensing device 204. A distance from thepoint of attachment of the fixation pins 610, 612 to the marked positionon the femur can then be recorded in the surgical orientation device172. The position can be based on capturing the markings 682 the probe678, 678B or probe inlay 676 by the camera 684, in combination withinertial data from the orientation sensing device 204.

The femur can be positioned in a neutral reference position with respectto flexion, abduction and rotation. This neutral position can berepresentative of a standing position of the patient.

The surgeon can position the distal end 680, 680B of the probe 678, 678Bat various anatomical landmarks. The surgeon can hold the hip stable. Insome methods, Point 1 of the system is the mounting point of one or morefixation pins 610, 612. Referring back to FIG. 39, each fixation pin610, 612 can be driven into the pelvis. In some techniques, one of thefixation pins 610, 612 is mounted to a pelvic bone at a landmark. Whenone of the fixation pins 610, 612 is coupled with a landmark, only twoadditional landmarks are acquired in some embodiments as discussedbelow. In some methods, the distal end 680, 680B of the probe 678, 678Bis placed at the contralateral ASIS landmark. The surgeon can enter aninput to register Point 2 (e.g., depress a button on surgicalorientation device 172). The surgical orientation device 172 canindicate that Point 2 was recorded. The probe 678, 678B can beimmobilized and the orientation of the orientation sensing device 204can be recorded by the surgical orientation device 172. Additionally,the distance that the probe 678, 678B is extended, as captured by thecamera 684, to contact the contralateral ASIS can be recorded by theorientation device 172.

The process to record the contralateral ASIS can be repeated for one ormore additional points. In some methods, the distal end 680, 680B of theprobe 678, 678B is placed at the pubic tubercle. The surgeon can enteran input to register Point 3 (e.g., depress a button on surgicalorientation device 172). The surgical orientation device 172 canindicate that Point 3 was recorded. In some methods, either pubictubercle may be used as a reference. The probe 678, 678B can beimmobilized and the orientation of the orientation sensing device 204can be recorded by the surgical orientation device 172. Additionally,the distance that the probe 678, 678B is extended, as captured by thecamera 684, to contact the pubic tubercle can be recorded by theorientation device 172.

When registering the anatomical points, the camera 684 captures an imageof the marking 682. The camera 684 can read the marking 682 to provideaccurate determination of the translational position of the probe 678,678B relative to the dock 662. The camera 684 can be directly above themarking 682. In some methods, the camera 684 can read a binary code ofthe marking 682.

In some methods, the orientation sensing device 204 converts the imageof the camera 684 into an extension measurement of the probe 678, 678B.In some embodiments, the surgical orientation device 172 converts theimage of the camera 684 into an extension measurement of the probe 678,678B. The distance related to the extension of the probe 678, 678B canbe used in conjunction with the orientation and positional data from theorientation sensing device 204. The surgical orientation device 172 canuse the length measurement from the camera 684 and the data from theorientation sensing device 204 to determine the location of the distalend 680, 680B of the probe 678, 678B. In some embodiments, the surgeonwill enter an input (e.g., depress a button) to collect data from theorientation sensing device 204. In some methods, the surgeon will enteran input (e.g., depress a button) to collect data from the camera 684.In some embodiments, the surgeon will enter an input (e.g., depress abutton) to collect data from the orientation sensing device 204 and thecamera 684 simultaneously. In some methods, the orientation sensingdevice 204 and/or the camera 684 will only send data if the orientationsensing device 204 is stable or non-moving.

Once the foregoing points of the pelvis have been navigated and the datarecorded into the surgical orientation device 172, the anterior pelvicplane can be calculated from data indicating the navigated points. Theorientation of the anterior pelvic plane is a baseline for placement ofthe cup portion of a hip prosthesis.

The orientation sensing device 204 and the surgical orientation device172 can at this point be used to guide placement of the cup in theprescribed orientation. The surgeon can set the angle of the cup. Laterin the procedure, the surgeon can check cup angle after the angle hasbeen set. The surgeon can remove the second assembly 606 from the firstassembly 604. The surgeon can remove the extension 670 from the thirdcoupler 668. The surgeon can couple the extension 670 to an impactor300B, shown in FIGS. 56A-56F. The impactor 300B can have the fourthcoupler 338B. This permits the orientation sensing device 204 to coupleto the fourth coupler 338B. The acetabular shell can be threaded ontothe shell adaptor, similar to FIG. 11C. The shell adaptor can be snappedonto the end of the impactor 300B, similar to FIG. 11B.

The acetabular shell can be inserted into the acetabulum and positionedat the desired angle. The surgical orientation device 172 can guide thesurgeon in setting the appropriate cup angle. The surgical orientationdevice 172 can graphically display when the orientation sensing device204 is located at the inclination and anterversion angles entered by thesurgeon. The surgical orientation device 172 can graphically display theinclination and anterversion angles as the orientation sensing device204 is moved. The surgeon can enter an input to set the desired angle(e.g., depress a button on surgical orientation device 172).

The inclination and anteversion cup angles can be displayed statically.The anatomic angles are those calculated by the system 600 based on thepelvic landmark registration. The table angles are those calculated bythe system 600 based on the initial positioning of the pelvis duringtable registration. The surgeon can check cup angle after the angles areset.

If femoral landmark Fm is acquired in the procedure prior to separatingthe natural joint, the same landmark can be acquired after theprosthetic joint is placed to confirm that the replacement of the jointhas not changed either the length of the leg, the off-set of the legfrom the trunk of the patient or both. Thereafter, the distal end 680,680B of the probe 678, 678B can be brought into contact with the samelandmark (e.g., Fm) acquired early in the procedure. The orientation ofthe orientation sensing device 204 and the extension of the probe 678,678B can be input into the surgical orientation device 172. These dataenable the surgical orientation device 172 to output amounts of changein leg length and leg offset.

In one variation described above in connection with the system 600, 600Band FIG. 24A, a plurality of points, e.g., three points, on the femurare acquired before and after the joint is replaced, for instance withthe use of the femur tracker 686. This approach enables a furtherconfirmation that the rotation orientation of the neck of the femurrelative to an axis extending through the center of the cupperpendicular to the plane of the acetabulum is unchanged after theprocedure.

The surgeon can register the home position. The surgeon can couple thesecond assembly 606, 606B to the first assembly 604, 604B as shown inFIGS. 39 and 40. The mount 672 can be coupled to the orientation sensingdevice 204 as described herein. The mount 646 can be coupled to thesurgical orientation device 172 as described herein. The surgeon canconfirm that the components of system 600, 600B are rigidly coupled. Thesurgeon can verify the parked configuration or home position. The distalend 680, 680B of the probe 678, 678B can be engaged with a point on theplatform 620 or cannula 621B. The platform 620 or cannula 621B caninclude the divot 630 as described herein. The divot 630 can be sized toaccept the distal end 680, 680B of the probe 678, 678B. The change inthe home position is displayed on the surgical orientation device 172.

C. Navigation Using Pre-Operative Imaging and Patient Specific Jigs

Although the foregoing approaches can improve the standard of carecurrently in place, further increases in accuracy and even betteroutcomes and streamlining of the procedure can be provided if the systemis configured to account for patient specific anatomical variability.

1. Patient Specific Jigs: Navigation Using Fixation Pins MountedTherethrough

FIG. 43 shows the placement of a hip movement tracking sensor 204 on apin 732 adjacent to the acetabulum. This position is not limiting, inthat the hip movement tracking sensor 204 can be mounted anywhere on thepelvis, but adjacent to the acetabulum is convenient. The pin 732 hasbeen placed with the aid of a pre-operative characterization of the hipof the specific patient. In these methods the pin 732 is placed withoutthe need for intra-operative landmark acquisition.

In one approach, a pre-operative three-dimensional characterization ofthe acetabulum is performed using any suitable technology, such as CTscan or MM. This pre-operative procedure can be performed to fullycharacterize the pelvis and, in some cases, the proximal femur.Thereafter, the shape, location and orientation of the acetabulum areknown. Also, the bony features around the acetabulum are known. Fromthis data, a custom jig 700 can be fabricated specific to the patient.The custom jig 700 not only has features that are specific to theindividual patient's anatomy but also a registration feature 702 thatwill be at a known orientation to the plane of the acetabulum and to theanterior pelvic plane.

FIG. 44 shows an example of the custom jig 700. The jig 700 has ananterior side 704 and a posterior side 708. The posterior side 708 isformed with an acetabular portion 712 configured to mate with at leastone feature of the acetabulum in a secure manner. For example, theacetabular portion 712 can fit snugly over the acetabular rim with acentral portion of the posterior side 708 positioned in the acetabulum.The jig 700 preferably has only one pre-defined orientation. A surfaceon a posterior portion of the jig can define a plane that corresponds toa preferred orientation angle of the cup post-implantation. One or morechannels 716 can be formed on the posterior side 708 that receive thelocal bony prominences of the acetabular rim only when the jig 700 is inthe proper position and orientation. In another approach, theregistration feature 702 of the jig 700 has a face or a hole that isoriented in the desired orientation for the shell or cup of the implant.Thus, once the jig 700 is placed, the sensing device 204 can bepositioned against the face or surface or, if coupled with a pin 732,the pin can be inserted into the hole. From the orientation of thedevice when so placed, the orientation of the acetabular rim or a proxythereof can be recorded in one or both of the devices 172, 204. The hole702 preferably extends from the anterior side 704 to the posterior side708 of the jig 700. The distance between the anterior and posteriorsurfaces 704, 708 provides the depth of the hole 702 being sufficient toguide a pin to specific anatomy along a specific direction.

FIG. 45 shows initial placement of the jig 700 in the acetabulum in anorientation dictated by the fit of the jig 700 over the anatomy. Theprofile of the posterior side 708 including the channel(s) 716 receivesthe specific patient's acetabular rim including local prominences andrecesses of the bone at and around the acetabulum. The hole 702 islocated on a peripheral projection 720 of the jig 700. The configurationof the projection 720 is such that the hole 702 is disposed over aspecific bone or bone region of the hip. In this example, the projection720 is configured to be disposed over the bone superior to theacetabulum. Other regions of bone around the acetabulum can be used ifsufficiently thick or strong and in a convenient position to not blockactions of the surgeon during the procedure. The precise location of theprojection 720 chosen can be determined by the pre-operative imaging andfactored into the forming the custom jig 700.

FIG. 46 shows that after the jig is placed the pin 732 can be placedthrough the hole 702. The pin 732 has a length that extends above theanterior surface 704 of the jig 700 such that the sensor 204 can bemounted thereto. Once the sensor 204 is mounted to the pin, the sensorcan track any movement of the pelvis during the procedure. There is noneed for registration of landmarks in this technique because theposition and orientation of the pin relative to the acetabulum and/or tothe anterior pelvic plane are known from the pre-operative imaging.

FIG. 47 shows that the plug 700 advantageously can include an alignmentguide 736 to control rotational orientation of the sensor 204 on the pin732. The alignment guide 736 can be a line extending along a specificdirection relative to the registration feature 702. As noted above, thesensing devices inside the sensor 204 can be sensitive to the directionof gravity. Tilting of the sensor about the pin 732 can change thereadings of these sensing devices. To eliminate sources of errorassociated with this sensitivity, the navigation system incorporatingthe sensor 204 can be programmed to assume that the sensor will be at aspecific rotation position about the longitudinal axis of the pin 732.The sensor 204 may be mechanically or visually aligned with the guidingmark 738 to assure that this assumption is met in use. In one variation,the sensor 204 has a laser that projects onto the jig 700 and can bealigned with the mark 736 to facilitate alignment. Alternatively, thepin 732 may be configured to only enter the hole in a unique orientation(for example, with an asymmetric non-circular cross-section), and toallow the sensor to mount to the pin in a unique orientation (byincluding asymmetric coupling features).

Once the sensor 204 is mounted to the pin 732, the jig 700 can beremoved from the surgical area. For example, the jig 700 can be made ofmaterial can be cut along a line 742 in a lateral edge of the jig. A sawor rongeur can be used to cut through the jig 700. Thereafter, themajority of the body of the jig 700 can be removed from the surgicalarea. FIG. 49 shows that in some methods, the projection 720 is left inplace so that the position and orientation of the sensor 204 is notdisrupted.

A second sensor 204 is attached to a cup impactor, which may be the sameas in FIGS. 11A-11C. The impactor guides the placement of the cup withreference to the signals from the sensor 204 mounted on the pin 732 onthe pelvis. Signals from the sensor on the impactor can be corrected ifmovement of the hip is detected by the sensor on the pin 732.

FIGS. 50-52 illustrate one way of implementing cannulated guide deliverymethods. Cannulated methods are advantageous in that once a guide memberis mounted, the tracking of orientation is simplified and may no longerbe necessary in some cases, which can eliminate accumulated errors,sensor drift, or erroneous readings of other sorts as a concern.

A custom jig 750 is formed by the process discussed above in connectionwith the jig 700. The jig 750 has many of the same components as thoseof the jig 700, including a registration feature 752 extending betweenthe anterior and posterior surfaces 754, 758. A guiding mark 738 can beprovided on the anterior surface 754 to align the sensor 204rotationally about the pin 732. The jig 750 also has a guide channel 762located generally centrally in the jig 750. The guide channel 762 has ananterior opening on the anterior surface 754, a posterior opening on theposterior surface 758, and a wall extending between these openings. Thewall is disposed about a central axis A. The position and orientation ofthe axis A can be determined based on the pre-operative characterizationof the acetabulum. In one embodiment, an MM or CT scan reveals anoptimal axis for delivering a prosthetic cup along. The wall forming theguide channel 762 is formed about the axis A which coincides with thisoptimal axis when the jig 750 is placed on the specific patient'sacetabulum.

FIG. 51 shows that the impactor 300A can then be advanced along the axisA into the guide channel 762. A distally facing shoulder 766 on theimpactor 300A can mate in a pre-defined way with the anterior surface754 and the entrance to the channel 762 and when so mated theorientation of the sensor 204 on the impactor 300A can be recorded. Inthis technique, the jig 750 is a cannula with the channel 762 configuredto receive the impactor 300A. If patient movement is possible, thesensor 204 on the pin 732 can be retained in place to track suchmovement. If not, the sensor 204 on the pin 732 can be removed. Thesensor 204 on the impactor 300A will have stored the orientation of theaxis A in memory and will be able to inform the user of any variance ofthe impactor from this axis. It is preferred to retain the sensor 204 onthe pin 732, as the orientation can only be accurate stored by thesensor 204 on the impactor 300A for a short time due to accumulatederror (e.g., drift) of some sensors, e.g., some lower cost gyroscopes.

In one variation, the impactor 300A has a central channel that coincideswith the axis A when the impactor is placed into the guide channel 762and the shoulder 766 abutted with the surface 754. A guide pin can beadvanced through this channel and into the acetabulum. The guide pin canbe lodged in the base of the acetabulum. The sensor 204 coupled with thepelvis by the pin 732 can be removed because the guide pin placedthrough the channel of the impactor 300A provides a mechanical way oftracking movement of the hip. Thereafter the impactor 300A with the cupmounted thereon can be slide over the guide pin and into place in theacetabulum.

In a further variation, the sensor 204 coupled with the impactor 300Acan also be removed. In this further variation, the guide pin isconfigured along with the cup to prevent tilting of the prosthetic cuprelative to the axis A. In particular, an interface between the guidemember and the cup of the hip prosthesis could be made to havesufficient length along the axis A that tilting is prevented by thisinterface. In some cases, the cup 360 is coupled to the impactor 300,300A. A variation of the impactor 300, 300A can be tubular or haveanother feature for interfacing with, e.g., tracking along the guide pinin the pelvis.

2. Patient Specific Jigs: Navigation Using Inertial Sensors Mounted onImpactor

FIGS. 53-60 shows another embodiment of a custom jig. The systemsdescribed herein can be used with a patient specific jig 1000, shown inFIG. 55. In some embodiments, the system 600, 600A, 600B or componentsthereof, can be used with the patient specific jig 1000.

Referring to FIG. 53, the system 600A can include a fixation base 602A.The fixation base 602A can include a platform 620A. The platform 620Acan include one or more holes 611A. The holes 611A can be sized toaccept a fastener 613A to secure the fixation base 602A to the pelvis.The fixation base 602A can include divot 630A. The divot 630A can be aregistration feature associated with a parked configuration or homeposition. Each fastener 613A can be driven into the ilium on the pelvis.As discussed further below, each fastener 613A can be coupled with otherbones in other techniques. For example, one of the fasteners 613A can becoupled with the ischium or the pubis. One of the fasteners 613A can becoupled at a point superior to the superior-most point on the acetabularrim. In some techniques, one of the fasteners 613A is about 10 mm abovethe superior-most point on the acetabular rim.

The fixation base 602A can include the first coupler 632. The firstcoupler 632 can couple to one or more components of the system 600A. Thesystem 600A can include the first assembly 604A shown in FIG. 54. Thefirst assembly 604A is rigidly connected to the hip in the illustratedconfiguration so that motion of the hip cause corresponding motion ofsensor(s) in the first assembly 604A as discussed below. The firstassembly 604A can include a pelvic bracket 638A. In the illustratedembodiment, the pelvic bracket 638A can be substantially vertical inuse, as shown in FIG. 54. The first assembly 604A can be designed tocouple with the first coupler 632 of the fixation base 602A.

The first assembly 604A can include an extension 644A. The extension 644can be coupled to the pelvic bracket 638A. The extension 644A caninclude a mount (not shown) designed to couple with the surgicalorientation device 172. The surgical orientation device 172 can includefeatures to mate with the mount (not shown). The surgical orientationdevice 172 is rigidly coupled to the extension 644A when engaged withthe mount.

The system 600A can include the second assembly 606A or a portionthereof. The second assembly 606A can include an extension 670. Theextension 670 can couple to the second coupler 648. The engagementbetween the second coupler 648 and the extension 670 minimizes orprevents relative movement therebetween to avoid any mechanical relativemovement during navigation procedures. The extension 670 can include amount 672 designed to couple with the orientation sensing device 204. Inthe illustrated embodiment, the mount 672 includes a lock and releaselever that can pivot relative to the extension 670. The orientationsensing device 204 can include features to mate with the lock andrelease lever. Other configurations are contemplated. The orientationsensing device 204 is rigidly coupled to the extension 670 when engagedwith the mount 672. In some methods of use, the system 600, or a portionthereof, is coupled to the pelvis instead of the system 600A. [0285] Thesurgeon can select the hip (e.g., right or left) using the surgicalorientating device 172. The surgeon can input the target cup inclinationangle into the surgical orientation device 172. The inclination anglecan be radiographic inclination as described herein. The surgeon caninput the target cup anteversion angle into the surgical orientationdevice 172. The anteversion angle can be radiographic anteversion asdescribed herein.

The second assembly 606 includes the extension 670 and the mount 672, asshown in FIG. 23A. The orientation sensing device 204 can be coupled tothe mount 672. The extension 670 can be coupled to the second coupler648. The orientation sensing device 204 and the surgical orientationdevice 172 can be calibrated as described herein. The system 600 can bemounted similar to system 600A shown in FIG. 54. The method step ofcoupling the orientation sensing device 204 with the second coupler 648can relate the orientation data of the orientation sensing device 204 toa reference frame of the surgical orientation device 172.

In some embodiments, a pre-operative three-dimensional characterizationof the acetabulum is performed using any suitable technology, such as CTscan or MM. This pre-operative procedure can be performed to fullycharacterize the pelvis and, in some cases, the proximal femur.Thereafter, the shape, location and orientation of the acetabulum areknown. Also, the bony features around the acetabulum are known. Fromthis data, the patient specific jig 1000 can be fabricated specific tothe patient. The patient specific jig 1000 not only has features thatare specific to the individual patient's anatomy but also a registrationfeature 1002 shown in FIG. 55 that will be at a known orientation to theplane of the acetabulum and to the anterior pelvic plane.

FIG. 55 shows an example of the patient specific jig 1000. The patientspecific jig 1000 has an anterior side 1004 and a posterior side 1008.The posterior side 1008 is formed with a three dimensional shapeconfigured to mate with at least one feature of the acetabulum in asecure manner. For example, an acetabular projection 1012 can beprovided that fits snugly over the acetabular rim with a central portionof the posterior side 1008 positioned in the acetabulum. The patientspecific jig 1000 preferably has only one pre-defined orientation. Asurface on a posterior side 1008 of the patient specific jig 1000 candefine a plane that corresponds to a preferred orientation angle of thecup post-implantation. One or more channels 1016 can be formed on theposterior side 1008 that receive the local bony prominences of theacetabular rim only when the patient specific jig 1000 is in the properposition and orientation.

In some embodiments, the registration feature 1002 of the patientspecific jig 1000 can include a recess, a hole, or a projection. In onemethod of using the illustrated embodiment, the orientation sensingdevice 204, not shown but described herein, is coupled to an impactor300B. The impactor 300B can be inserted into the registration feature1002. Thus, once the patient specific jig 1000 is placed, theorientation sensing device 204 can be positioned in a known orientationrelative to the registration feature 1002. From the orientation of theorientation sensing device 204 when so placed, the orientation of theacetabular rim or a proxy thereof can be recorded in one or both of thedevices 172, 204. The registration feature 1002 preferably extends fromthe anterior side 1004 toward the posterior side 1008 of the patientspecific jig 1000. The distance between the anterior and posteriorsurfaces 1004, 1008 provides the depth of the registration feature 1002being sufficient to securely couple to the impactor 300B. In otherembodiments, the registration feature 1002 extends anteriorly of theanterior side 1004 of the jig 1000, e.g., as a projection or post.

FIGS. 56A-56F show the impactor 300B. The impactor 300B can besubstantially similar to impactors described herein, and can include anyfeatures of impactors described herein. The shaft 316B can includeplurality of flats 350B on the distal end of the shaft 316B as shown inFIG. 56F. The flats 350B permit proximal-distal sliding of theregistration feature 1002 of the patient specific jig 1000 over thedistal end of the shaft 316B into or out of the feature 1002 shown inFIG. 57. In some embodiments, a detent device 351B or other lockingmechanism is provided between the shaft 316B and the registrationfeature 1002. This mechanism may prevent inadvertent release of thepatient specific jig 1000 from the impactor 300B. The flats prevent theshaft 316B from rotating relative to the patient specific jig 1000. Theflats 350B can enable many discrete alternate relative angular positionsof the patient specific jig 1000 to the shaft 316B. The number oforientations of the impactor 300B relative to the patient specific jig1000 can depend on the number of flats.

FIG. 58A-58B shows initial placement of the patient specific jig 1000 inthe acetabulum in an orientation dictated by the fit of the patientspecific jig 1000 over the anatomy. The method can include the step ofcoupling the patient specific jig 1000 to a rim of the acetabulum. Theprofile of the posterior side 1008 including the channel(s) 1016, shownin FIG. 55, receives the specific patient's acetabular rim includinglocal prominences and recesses of the bone at and around the acetabulum.The acetabular projection 1012 can be peripheral projection of thepatient specific jig 1000. The configuration of the acetabularprojection 1012 is such that the acetabular projection 1012 is disposedover a specific bone or bone region of the hip. In this example, theacetabular projection 1012 is configured to be disposed over the bonesuperior to the acetabulum. Other regions of bone around the acetabulumcan be used if sufficiently thick or strong and in a convenient positionto not block actions of the surgeon during the procedure. The preciselocation of the acetabular projection 1012 chosen can be determined bythe pre-operative imaging and factored into the forming the patientspecific jig 1000.

The impactor 300B can be placed in the registration feature 1002 beforeor after the patient specific jig 1000 is placed in the acetabulum. Theimpactor 300B has a length that extends above the anterior surface 1004of the patient specific jig 1000 such that the sensor 204 can be mountedthereto. Referring back to FIG. 54, the orientation sensing device 204can be undocked from the second coupler 648. The orientation sensingdevice 204 can thereafter docked to the fourth coupler 638B of theimpactor 300B. The fourth coupler is shown in FIG. 58B.

The patient specific jig 1000 can include an alignment guide 1038 tocontrol rotational orientation of the orientation sensing device 204 onthe impactor 300B. The alignment guide 1038 can be a line extendingalong a specific direction relative to the registration feature 1002. Asnoted above, the orientation sensing device 204 can be sensitive to thedirection of gravity. The rotation of the orientation sensing device 204about the impactor 300B can change the readings of these sensingdevices. To eliminate sources of error associated with this sensitivity,the navigation system incorporating the orientation sensing device 204can be programmed to assume that the orientation sensing device 204 willbe at a specific rotation position around the longitudinal axis of theimpactor 300B. The alignment guide 1038 can correspond to the desiredrotation position orientation sensing device 204.

In the illustrated embodiment, the fourth coupler 338B may bemechanically or visually aligned with the alignment guide 1038 to assurethat this assumption is met in use. In the illustrated embodiment, thealignment guide 1038 is an elongate arrow. The elongate arrow can alignwith the longitudinal axis of the fourth coupler 338B. The surgeon canlook down the impactor 300B from the proximal end to the distal end. Thesurgeon can verify the alignment of the alignment guide 1038 and thefourth coupler 338B. The alignment between the alignment guide 1038 andthe fourth coupler 338B constrains the orientation sensing device 204 inthe third degree of freedom. The surgical orientation device 172 can beprogramed with this known angle of the orientation sensing device 204when the impactor 300B is coupled to the patient specific jig 1000. Insome embodiments, the surgeon will enter an input (e.g., depress abutton) when the patient specific jig 1000 is seated with the impactor300B and the orientation sensing device 204 coupled thereto. Thesurgical orientation device 172 can calculate the orientation of thesurgical orientation device 172 relative to the pelvis when the input ispressed. This step may replace registering the pelvic landmarks with theprobe, as discussed herein.

In some embodiments, the orientation sensing device 204 has a laser thatprojects onto the patient specific jig 1000 and can be aligned with thealignment guide 1038 to facilitate alignment. Alternatively, theimpactor 300B may be configured to only enter the registration feature1002 in a unique orientation (for example, with an asymmetricnon-circular cross-section), and to allow the orientation sensing device204 to mount to the patient specific jig 1000 in a unique orientation(by including asymmetric coupling features).

Once the orientation sensing device 204 is mounted to the impactor 300B,the surgeon can hold the orientation sensing device 204 steady. In someembodiments, the surgeon will enter an input (e.g., depress a button) tocollect data from orientation sensing device 204. The data can includethe impactor angle. The impactor angle can be fixed during the methodsuch that the angle can be known to the system or in the method indirecting placement of the hip implant components. In some embodiments,the impactor angle can be 10° inclination, 20° inclination, 30°inclination, 40° inclination, 50° inclination, 60° inclination, 70°inclination, 80° inclination, 90° inclination, between 30°-70°inclination, between 40°-60° inclination, etc. In some embodiments, theimpactor angle can be 10° anteversion, 20° anteversion, 30° anteversion,40° anteversion 50° anteversion, 60° anteversion, 70° anteversion, 80°anteversion, 90° anteversion, between 0°-40° anteversion, between10°-30° anteversion, etc. In the illustrated embodiment, the impactorangle is 50° inclination, 20° anteversion. The impactor angle can bebased upon the orientation of the registration feature 1002 relative tothe patient specific jig 1000. The impactor angle can be set duringfabrication of the patient specific jig 1000. In some embodiments, theimpactor angle must be known by the software of the surgical orientationdevice 172. In some embodiments, the impactor angle is constant for alljigs and hard-coded into the surgical orientation device 172. In someembodiments, the impactor angle can be input by the user at the time ofsurgery. The surgeon can input the impactor angle into the surgicalorientation device 172 using the user interface as described herein.

The orientation sensing device 204 can transmit orientation andpositional data to the surgical orientation device 172. The surgicalorientation device 172 can register the guide angle when the orientationsensing device 204 is coupled to the patient specific jig 1000. In somemethods, the surgical orientation device 172 can perform a biaselimination step. The surgical orientation device 172 can track motionof the pelvis and to generate an output that eliminates error due to themovement of the pelvis. The surgical orientation device 172 can includea display providing a user interface. The method can include the step ofregistering the orientation of a proxy for the plane of the acetabularrim using the orientation sensing device 204 coupled with the patientspecific jig 1000.

The orientation sensing device 204 can track any movement of the pelvisduring the procedure. There is no need for registration of landmarks inthis technique because the position and orientation of the impactor 300Band/or orientation sensing device 204 relative to the acetabulum and/orto the anterior pelvic plane are known from the pre-operative imaging.From the known orientation of the orientation sensing device 204 withrespect to the pelvis, the system can calculate the orientation of thesurgical orientation device 172 with respect to the pelvis.

The surgeon can remove the patient specific guide 1000 from the patientas shown in FIG. 59. The surgeon can remove the impactor 300B from thepatient specific guide 1000. The surgeon can prepare the acetabulum. Insome embodiments, the surgeon can ream the acetabulum. The impactor 300Bcan be used to position a shell in the acetabulum. The shaft 316B caninclude plurality of flats 350B on the distal end of the shaft 316A asshown in FIG. 56F. Referring to FIGS. 11B-C and 60, the impactorsdescribed herein can be coupled with the tip component 348. FIG. 11Cshows that the tip component 348 can have a recess 352 formed on theproximal side thereof. The recess 352 can comprises a plurality of flats350B corresponding to a plurality of flats 350B on the distal end of theshaft 316B. The flats 350B permit proximal-distal sliding of the recess352 over the distal end of the shaft 316B. Preferably a detent device orother mechanism is provided between the tip component 348 and the shaft316B so that the tip component 348 does not disengage. The flats 350Bprevent the tip components 348 from rotating relative to the shaft 316BThe engagement device 356 comprises threads in one embodiment so thatthe cup of the prosthetic hip can be screwed onto the distal end of thetip component 348. The flats enable many discrete alternate relativeangular positions of the tip component 348 (and hence the cup) to theshaft 316B. A plurality of flutes or elongate axial ridges 364 on theouter surface of the tip component 348 enable the user to securely graspthe tip component for mounting and dismounting the tip component on theshaft 316B. The surgeon can position the cup in the acetabulum. Thesurgeon can hold the impactor 300B steady.

During orienting, inertial data from the orientation sensing device 204can be used to confirm a proper orientation of the acetabular cup. Thesurgical orientation device 172 can register the guide angle when thecup is positioned within the acetabulum. In some embodiments, thesurgeon will enter an input (e.g., depress a button) to collect datafrom orientation sensing device 204. The surgical orientation device 172can display the cup angle. The surgeon can move the cup to change theinclination angle. The surgeon can move the cup to change theanteversion angle. The surgeon can move the shell until the inclinationangle and anterversion angle matches the preoperative angles. The methodcan include the step of changing the orientation of the impactor 300B inresponse to an output reflecting the inertial data generated by theorientation sensing device 204. In the illustrated embodiment, thepreoperative impactor angle can be 50° inclination, 20° anteversion. Insome methods, the surgical orientation device 172 can perform a biaselimination step. In some methods, the surgical orientation device 172can perform a gyro propagation step. Examples of bias elimination stepsand gyro propagation steps are discussed in U.S. Ser. No. 13/011,815,filed Jan. 21, 2011, which is hereby incorporated by reference for thisand all other purposes. The surgical orientation device 172 and/or theorientation sensing device 204 can include any of the softwarealgorithms described therein.

The surgeon can seat the cup in the acetabulum using the impactor 300B.The surgical orientation device 172 can remain coupled to the firstassembly 604. The orientation sensing device 204 can be coupled to thefourth coupler 338B on the impactor 300B, as shown in FIG. 60.

In some embodiments, the surgeon will enter an input (e.g., depress abutton) to collect data from orientation sensing device. The data caninclude the impactor angle. The impactor angle can be known. At thisstep, the impactor angle can be 50° inclination, 20° anteversion. Theimpactor angle can be based upon the orientation of the registrationfeature 1002 relative to the patient specific jig 1000. The impactorangle can be set during fabrication of the patient specific jig 1000. Insome embodiments, the impactor 300B can be rotated to a set number ofpositions within the registration feature 1002. The impactor 300B can berotated by the surgeon to align a feature of the impactor 300B with thealignment guide 1038. The fourth coupler 338B can be aligned with thealignment guide 1038. The impactor 300B can be positioned such that thefourth coupler 338B can be pointed superiorly. In other embodiments, theimpactor 300B has a single orientation within the registration feature1002. The position of the orientation sensing device 204 can betherefore known relative to the patient specific jig 1000, when theorientation sensing device 204 is coupled to the impactor 300B. Thesurgical orientation device 172 can calculate and record the orientationof the surgical orientation device 172 with respect to the pelvis.

The impactor 300B may be struck to seat the implant. In someembodiments, the orientation sensing device 204 remains on the impactor300B as the impactor 300B is struck. Referring to FIG. 60, the impactor300B has a shell 312B that is moveable relative to the shaft 316B. Theshell 312B can include the fourth coupler 338B that can couple to theorientation sensing device 204. The movability of the shell 312B helpsto isolate the orientation sensing device 204 from the forces that aretransmitted through the impactor 300B. These forces are applied by amallet or other device for forcibly moving the cup into position. Byproviding at least some force isolation between the shell 312 and theorientation sensing device 204, impact on the sensors in the orientationsensing device 204 can be reduced. Excessive force being applied to theorientation sensing device 204 can put the orientation sensing device204 out of service, for example until synched with the surgicalorientation device 172. The movement of a shell 312B is cushioned by aplurality of spring members 340B, 344B which are configured to absorb atleast some of the shock of the impact on the impactor 300B.

3. Custom Jigs: Navigation Using Fixation Pins Mounted Therethrough

FIGS. 61-63 show an example of the custom jig 1100. The jig 1100 has ananterior side 1104 and a posterior side 1108. The posterior side 1108 isformed with an acetabular portion 1112 configured to mate with at leastone feature of the acetabulum in a secure manner. The jig 1100preferably has only one pre-defined orientation. In some embodiments, aregistration feature 1102 of the jig 1100 has a plurality of, e.g., two,holes. The registration feature 1102 can be located on the acetabularportion 1112 or any other portion of the custom jig 1100. The holes aresized to accept fixation pins 610, 612 of the system 600. In a variationof FIGS. 44-52, a patient specific guide can be provided with aregistration feature including a single hole. The hole or holes canaccept fixation pin(s) 610 in a single orientation relative to thepatient or relative to the custom jig 1100. The method can include thestep of inserting at least a fixation pin 610 through the patientspecific jig 700 or jig 1100 along an axis disposed at a pre-definedangle corresponding to the reference frame of the surgical orientationdevice 172.

The first hole 1105 of the registration feature 1102 can accept afixation pin 610 and a second hole 1107 can accept fixation pin 612. Thesystem 600 can be placed in a single orientation relative to the customjig 1100. Thus, once the jig 1100 is placed, the surgical orientationdevice 172 and/or the orientation sensing device 204 can be positionedin a known orientation. In some embodiments, from the orientation of thesystem 600 when so placed, the orientation of the acetabular rim or aproxy thereof can be recorded in one or both of the devices 172, 204. Insome embodiments, the reference frame can be based directly on moregeneral pelvic landmarks such as the anterior pelvic plane. Theacetabular rim or a proxy can be used as an intermediate step to get tothe reference frame based directly on more general pelvic landmarks. Theregistration feature 1102 preferably extends from the anterior side 1104to the posterior side 1108 of the jig 1100. The distance between theanterior and posterior surfaces 1104, 1108 provides the depth of theholes 1105, 1107 being sufficient to guide the fixation pins 610, 612 tospecific anatomy along a specific direction. The method can include thestep of inserting at least two fixation pins 610, 612 through thepatient specific jig 1100 along axes disposed at a pre-defined anglecorresponding to the reference frame of the surgical orientation device172.

Once the devices 172, 204 are mounted to the system 600, the sensors cantrack any movement of the pelvis during the procedure. There is no needfor registration of landmarks in this technique because the position andorientation of the fixation pins 610, 612 relative to the acetabulumand/or to the anterior pelvic plane are known from the pre-operativeimaging.

4. Navigation Using Inertial Sensors and Pre-Operative Imaging

In another technique using less comprehensive imaging, a correspondencebetween one or more linear dimensions and an angle can be exploited toenhance accuracy. For example, a clinician can use an X-ray or otherstandard radiographic imaging device to provide an anterior pelvic boneimage. This image can be read to derive the location of the anteriorpelvic plane and a dimension on the anatomy. For example, an anglebetween top and bottom landmarks around the acetabulum (as furtherdescribe below) and a trans-ischial line or other anatomicmedial-lateral reference line can be a useful patient specific variableto minimize patient-to-patient variation in at least one relevant angle,e.g., the abduction angle.

Patient specific data can be provided for use by the surgeon based onbest medical judgment. For example, any of the systems herein can beused in a mode that is based on broad population studies. Such studiescan define a distribution of patients with sufficient clarity and detailto enable significant improvement over the current standard of care. Inone mode, the dimensions taken from radiograph or CT can be used toinform the surgeon whether some patient specific adjustments should beconsidered. Alternatively, patient specific adjustments can be codedinto the system described herein so that they are transparent to thedoctor. Such adjustments can be downloaded to either or both of thedevices 172, 204 or into a separate monitor or control device thatcommunicates wirelessly with the devices 172, 204. Thus, the systemdescribed herein can either fully implement patient specific adjustment,e.g., for anteversion, abduction, leg length, joint offset, or otherparameter or can enable the surgeon to make a judgment as to whether todo so.

FIG. 68 illustrates an example of a pre-operative image that can be usedin one technique. The lines 380 point to landmarks which are usedintraoperatively and are also visible in an anterior pelvic radiograph.The top landmark 380A is about 1 cm superior to most superior point ofacetabulum. In another approach, the top landmark 380A can be the mostsuperior point on the acetabular rim. The bottom landmark 380B isadjacent to or at the acetabular notch (tear drop). An angle betweenline 382 and the line 384 is a patient-specific abduction of line formedby landmarks, which can be entered into an interface of the system 100(or the other systems herein) at time of surgery to provide patientspecific reference frame. Line 384 may be any anatomic medial-lateralreference line. Examples include trans-ischial line and line across theinferior borders of the obturator foramina (shown in FIG. 68).

5. Navigation Using Drift Insensitive Inertial Sensors

In one variation, one or both of the devices 172, 204 can comprise onlyaccelerometers and can be configured as tilt meters, or the devicescould be put into a mode that relies mostly on the accelerometer data orotherwise be configured to be insensitive to accumulated errors thatarise from integration of data. If the patient is set in a reproducibleand stable position, patient movement and mis-orientation can beeliminated. This enables some methods to be performed without using ratesensor data. In one variation of this tilt-meter approach, one or bothof the sensors 172, 204 can be configured to inform the surgeon if acondition is sensed that suggests a landmark acquisition approach wouldyield a superior alignment outcome. This method can advantageously beused for procedures that do not require complex movements, like freehandmotions. Where freehand motion is involved, incorporating someindication of heading (gyroscopes, magnetometer, or other indication ofheading) would be useful.

6. Navigation Using Inertial Sensors to Track Motion to Define aPatient-Specific Safe Zone

In another technique illustrated by FIG. 64, a patient-specific “safezone” is defined by recording the patient's natural range of motion ofone more of the patient's joints. For example, if a hip procedure is tobe performed, the patient's range of motion can be recordedpre-operatively. If the hip to be replaced is not overly arthritic, therange of motion can be determined on the hip to be replaced. If therange of motion of the hip to be replaced is unnatural due to diseasestate, the contralateral hip can be characterized.

In one hip replacement technique a sensor S is coupled with the femur.The sensor can be coupled above the knee to prevent movements at theknee from affecting the measurements made. The sensor S can be connectedbelow knee if the knee is immobilized. The sensor S can be initializedand otherwise prepared to record accurate readings. Thereafter one ormore movements of the hip joint can be performed with the output of thesensor recorded and processed. The movements can include, for example,movement in anterior and posterior (A-P) directions to the full extentof the range of motion and movement in medial and lateral (M-L)directions to the full extent of the range of motion. These motionsdefine the patient's natural range of motions in these planes.

Based on the extents of motion in the A-P and M-L directions, a cone ofmotion CM can be defined. The cone of motion CM can be defined asoriginating at a point defined as the center of rotation of the femoralhead and extending out from the acetabulum to a circular base located adistance from the center of rotation equal to the distance to the mountpoint of the sensor. The circular base can be defined as having a radiusequal to the average extent of motion in the A-P and M-L directions. InFIG. 64, the cone of motion is shown on the contralateral side forclarity. As noted above, the data collected to estimate the cone ofmotion can be based on the leg to be treated or the contralateral leg.

Placement of the cup of the hip prosthesis is dictated by some metric ofcentering within the cone of motion. For example, the cup can becentered such that an axis extending perpendicular to the plane of theentrance to the cup crosses the circular base of the cone of motionprecise in the center of the cone. In some systems, the orientation ofthe cup is controlled such that the crossing point of the axis soprojecting is closer to the center of the circular base than it is tothe periphery of the circular base. In other systems, the orientation ofthe cup is controlled such that the crossing point of the axis soprojecting is within a distance from the center point that is less than25% of the radius of the circular base.

In a class of patients, the movement of the hip is not symmetrical ineach of the A-P and M-L directions. As such, the cone of motion can havea more complex geometry. For example, the cone of motion can originateat the center of rotation of the femoral head and extend to a basehaving an oblong shape, for example shortened in the medial direction,but longer in the lateral, anterior, and/or posterior directions.Various metrics of “within the safe zone” can be defined based on theseirregular shaped cones. For example the geometric center of a complexbase shape can be calculated and the cup of the prosthetic joint can becentered such that an axis extending perpendicular to the plane of theentrance to the cup crosses the irregular shaped base of the cone ofmotion at or within some maximum distance of the centroid of the cone.

Any suitable set of motions can be used to obtain the center of rotationof the femoral head and/or the boundaries of the base of the cone ofmotion. Examples of methods for determining the center of rotation of afemoral head using inertial sensors are discussed in U.S. Pat. No.8,118,815, which is hereby incorporated by reference for this and allother purposes. A more complete perimeter of the base of the cone ofmotion can be directly recorded using sensors that are capable oftracking both position and orientation. For example, several otherpoints between the A-P and M-L direction can be taken so that six,eight, ten, twelve or more extents are recorded. In other embodiments,arcuate motions of along all or portions of the perimeter of the base ofthe cone of motion can be traced and recorded. Because several degreesof freedom of the sensor S are constrained, the sensor can operate basedon accelerometers only in some approaches, which simplifies sensor S andenables it to be disposable and/or less expensive to make. Suchapproaches may be most accurate if rotations about a vertical axis areminimized or eliminated.

In one embodiment, the procedure illustrated in FIG. 64 generates anorigin and a direction that can be input to a cup placement system. Theorigin can be the center of rotation of the femoral head and thecorresponding center of rotation of a prosthetic socket. The directioncan be a line connecting the origin and the point of intersection withthe base of the cone of motion. This data is transferred to a cupplacement system, such as any of those discussed above. For example, theimpactor 300A can include the sensor 204 to which this data has beensaved. Thereafter movements of the impactor 300A can be tracked withreference to this origin and direction to assure proper placement of thecup. Such placement can be with the aid of a patient movement trackingsensor pinned to the pelvis for example.

In other embodiments, cannulated systems can be used to minimize thenumber of steps during which inertial sensors are used. For example,once the origin and direction of the axis connecting the center ofrotation and the intersection with the base of the cone of motion aredetermined, a guide member can be placed via a cannulated impactor (orother cannula). The guide member can dock with an impactor-mounted cup.The cup can be slid over the guide member into place in the acetabulum.The direction and origin information collected in the steps illustratedby FIG. 64 are preserved by the guide member and by the tilt preventingfeatures on the guide member and/or prosthetic cup.

If the patient's joint is subject to extensive disease, a cone of motioncan be established by a combination of data collected in motions similarto those discussed above in connection with FIG. 64 and pre-operativeimaging. For example, X-rays can be taken when the femoral neck is movedclose to the acetabular rim to supplement some of the data pointsdefining the cone of motion. Thus, the cone of motion can be in partestablished by inertial sensing and in part by imaging to characterizethe native anatomy.

D. Adaptable Systems for Anterior or Posterior Approach

The systems described herein can be adapted for use in the anteriorapproach, the posterior approach or both the anterior and posteriorapproach. As one example, system 600 is shown herein mounted for aposterior approach in FIG. 18, the anterior approach in FIG. 39, and incombination with a patient specific jig in FIG. 63.

FIGS. 69-72 illustrate a system 900 for navigating a hip procedure. Thesystem 900 can be adapted for use in both the anterior approach and theposterior approach. The system 900 can be similar to some of thosediscussed above. But, while some of the foregoing systems arespecialized for a particular approach, the system 900 includes a firstsub-system 900A adapted for a posterior approach and a second sub-system900B adapted for an anterior approach. As discussed more below, bothsystems 900A, 900B are configured to enable navigation to be conductedwithout requiring gyroscopic or other sensors that are subject toaccumulated error (drift). This refinement makes the system simpler toimplement and to use in a wider variety of settings and with morepatients.

The system 900A includes a jig 904A that is adapted for hip jointnavigation from a posterior approach. The jig 904A is similar in somerespects to the jig 454, and any consistent description thereof isincorporated herein. The jig 904A includes a platform 908, a cannulacoupling device 912, and a registration jig mounting feature 914. Theplatform 908 can have any shape, but in some implementations can beelongate, e.g., having a first end 916 and a second end 920. Theelongate shape enables at least a portion of the jig 904A to be lowprofile in one direction and to provide a plurality of positions along alength for coupling devices to the jig. The first end 916 is configuredto be oriented inferiorly and the second end 920 to be orientedsuperiorly when the navigation jig is applied to the patient. Themedial-lateral dimensions or extent can be minimized to not obstruct thesurgical field or the surgeon.

The cannula coupling device 912 is disposed adjacent to the first end916 and is configured to enable a cannula 924 to be held adjacent to abottom surface of the platform 908. The cannula 924 can have a topsurface connected to a bottom surface of the platform 908. A connectionbetween these components can be secured by a device disposed abovewithin or below the platform 908. In one form, a proximal structure ofthe cannula 924 can be received within a bottom recess of the platform908 and can be held within the recess by a compression device, such as aset screw S. Details of several variants of cannula coupling devices 912are discussed below in connection with FIGS. 73-75B. A connection to abone adjacent to a hip joint is made through the cannula 924. Forexample, a pin 928 can be placed through the platform 908 and thecannula 924 into the bone.

An anterior approach cannula 926 is shown in FIGS. 71 and 72 and issimilar to the cannula 516, the description of which is incorporatedherein. The description of the cannula coupling device 912 appliesequally to the cannula 924 for posterior approach and to the cannula 926for anterior approach.

The registration jig mounting feature 914 is disposed on a top surface932 of the platform 908 adjacent to the first end 916. In one form, themounting feature 914 includes an elevated portion of the platform. Themounting feature can include one or more, e.g., two recesses into whichpins can be received. In one embodiment, the elevated portion includes awindow, e.g., a through hole, for viewing such a pin to confirm correctplacement. As illustrated in FIG. 73, in one variant, a circular recesscan be provided for a first pin and an U-shaped slot can be provided foranother pin or member.

The hip navigation jig 904A also includes registration jig 940. Theregistration jig 940 can have some features similar to those discussedabove. The registration jig 940 includes an upright member 942, arotatable member 948, and a probe 952. The upright member 942 isconfigured to be detachably coupled to the platform 908 at theregistration jig mounting feature 914. For example, a plurality of(e.g., two) pins can project from a lower surface of the upright member942, the pins being configured to be received in corresponding recessesin the registration jig mounting feature 914. One of such pins isvisible through the window in the registration jig mounting feature 914seen in FIG. 70. The upright member 942 includes a first portion 944 anda second portion 946 disposed above the first portion 944. The firstportion 944 is substantially vertical and increases the elevation of thesecond portion 946 when the registration jig 940 is mounted to theregistration jig mounting feature 914. The second portion 946 isinclined away from a vertical longitudinal axis of the first portion944. The incline of the second portion 946 provides several advantages.It enables the upright member 942 to be out of the way of the range ofmotion of the probe 952, as discussed below. This is important becausethe probe 952 has to be able to easily and quickly reach a plurality ofanatomical features.

The incline of the second portion 946 also provides a simple way toincline an angle of rotation of the rotatable member 948 relative to avertical axis. The rotatable member 948 is coupled with the uprightmember 942 for rotation about an axis A that is not vertical when thejig is mounted to the bone adjacent to a hip joint and the uprightmember is disposed generally vertically. This arrangement is one way toenable a navigation system employing inertial sensors to eliminate theneed to manage sensor drift. As discussed above, certain sensors, suchas gyroscopes, are more subject to accumulated errors (drift). Theorientation of the axis A enables the jig 904 to be used in a systemthat includes accelerometers and other sensors that are sufficientlysensitive if activated and moved about axes that are not vertical.

As in the registration devices discussed above, other degrees of freedomof rotation and position can be provided in the registration jig 940 andsuch description is incorporated here.

The probe 952 had a tip 956 for engaging anatomy. The anatomy engagingtip 956 is disposed at a distal end of an elongate body 960 coupled withthe rotatable member for rotation about the axis. The orientation andposition of the elongate body 960 of the probe can be adjusted to bringthe anatomy engaging tip into contact with a plurality of anatomicallandmarks during a landmark acquisition maneuver. Such adjustments canbe by sliding through a sliding support, similar to those hereinbeforedescribed.

The upright member 942 can include a cradle 954 that allows the elongatebody 960 of the probe 952 to be held in place when not in use during aprocedure. The cradle 954 can be used to latch the sensor 204, asdiscussed above. In various implementations, the system 900 does notrequire any steps of zeroing, however, since the sensors are configuredto be generally drift insensitive. Eliminating sensitivity to drift canbe achieved by configuring the sensor 204 as a tilt meter, and/or byusing any sort of inertial sensor that will not introduce excessiveerror due to drift during the procedure time. As such, even sensors thathave some drift can be used, so long as their accumulation of error doesnot reach a significant level until during the procedure. The cradle 954could be used to zero error if a procedure was unexpectedly long and thesensor were subject to some drift. In one advantageous embodiment, thesensor 204 can operate solely with signals from accelerometers, whichare insensitive to drift.

FIGS. 69-72 show that the systems 900A, 900B can include one or moresensors for detecting orientation of the probe 952. The sensors can takeany form, e.g., can include the surgical orientation device 172 and thesensor 204 discussed above. Accordingly, the jig 904 can include asensor mounting feature 962 disposed on the platform 908. Where theplatform is elongate, the sensor mounting feature 962 can be disposed atthe second end 920. Another advantage of the jig 904A, 904B is that itis symmetrical and can be used on both hips. The jig 904A, 904B thus canhave a single sensor mounting feature disposed on a plane of symmetry.If the platform 908 is elongate, the sensor mounting feature 962 can belocated on a vertical mid-plane of the platform. Vertical here refers tothe orientation of the jig 904A, 904B when applied to the hip in aposterior or anterior approach.

The registration jig 940 can include a sensor mounting feature 964disposed thereon for movement with the probe 952. For example, thesensor mounting feature 964 can be located at a proximal end of theelongate body 960. This location is one of convenience, placing thesensor 204 at the proximal end. However, the sensor mounting feature 964and the sensor 204 could be located on a side surface of the elongatebody 960.

As discussed herein, the orientation of the axis of rotation A of therotatable member 948 enables the change of orientation of the sensor 204to be other than in the horizontal plane. This is accomplished byorienting the axis A other than in the vertical direction. With thisarrangement, it is possible to configure at least the sensor 204 as atilt meter, e.g., using primarily or only accelerometers to output asignal indicative of orientation of a component, such as of the prove952. Example of angles or ranges of angles of the axis A that can beprovided include about 20 degrees from horizontal, about 30 degrees fromhorizontal, about 45 degrees from horizontal, at less than about 60degrees from horizontal.

FIG. 70 shows a further feature of the system 900A, which includes thejig 904A and the cannula 924. The cannula 924 is adapted for posteriorapproach is similar to or the same as the hollow fixation member 466. Anupper or first end of the cannula 924 is configured to couple with thecannula coupling device 912, such as by a set screw as discussed above.A second end of the cannula 924 is configured to couple with a boneadjacent to the hip joint. The bone can be any of those discussed abovefor coupling the fixation member 466 or other analogous structuresdiscussed in any embodiments above. A home point feature 968 is disposedadjacent to the second (lower) end of the cannula 924. The home pointfeature 968 is in a predefined, known position and can receive theanatomy engaging tip 956 of the probe 952. When these structurescontact, they are in a predefined position and orientation. The homepoint feature 968 can be similar to the registration feature 473discussed above.

Because the system 900 can be adapted for posterior approach or foranterior approach (discussed below), the cannula 924 should be maderemovable from the platform 908 in the operating room or at a back tablein preparation for surgery. As such, the connection between the cannula924 and the platform 908 can be made orientation specific. This reducesa potential source of operator error, i.e., the home point feature 968always faces toward the surgical field from the hip bone attachmentlocation, e.g., faces inferiorly if the jig 904 is mounted to a superiorlocation of the surgical field. For example, a projection on a proximalportion of the cannula 924 and a corresponding projection in a recess onthe lower side of the platform 908 can define only one rotationalorientation of the cannula relative to the platform in which thesecomponents can be coupled.

As discussed above, the cannula 926 is provided in the system 900 toenable a surgeon to switch to an anterior approach. Anterior approach isdiscussed in great detail above, e.g., in connection with FIGS. 34-42,which description are incorporated here as well. The system 900B differsfrom the system 500 in that the orientation of the axis A of rotation inthe system 900B is not vertical, as discussed above. As such, thesensors can be greatly simplified compared to the system 500. Thecannula 926 has a home point feature 968B. The home point feature 968Bis in a predefined, known position and can receive the anatomy engagingtip 956 of the probe 952. When these structures contact, they are in apredefined position and orientation. The home point feature 968B can besimilar to the registration feature 473 discussed above. The cannula 926and the platform 908 can be configured for limited, e.g., only one,rotational position of attachment. This assures that when the jig 904Bis assembled in the operating room or back table that the jig 904B willbe properly set up.

In one method to maximize the accuracy of the landmark acquisition, jig904B is coupled with the patient in an anterior approach. The tip 956 isput into contact with the home point feature 968B. Thereafter, userinput can be applied to the surgical orientation device 172A to indicatethat the tip 956 is in the home point feature 968B. Thereafter, thesystem registers movements and landmark acquisition in the mannerdiscussed above. These data provide a basis to guide the placement ofthe acetabular cup, as discussed above.

The placement of the acetabular cup using a device such as the impactor300A can be an operation that benefits from inertial sensors that mayinclude one or more drift-sensitive sensors, e.g., gyroscopes. Thesystem 900 provides a calibration mount 998 for coupling a sensor 204 ina known, fixed position and orientation relative to the surgicalorientation device 172A. The calibration mount 998 is a docking devicethat positions the sensor 204 just prior to a step of eliminating anypotential source of accumulated error, e.g., zeroing a drift-sensitivesensor. FIG. 69-70 show that they system 900A can include two sensors204, one mounted to the registration jig 940 and one to the calibrationmount 998. These two sensors 204 can be identical or can be dedicatedfor their specific function. FIGS. 71 and 72 shows only one sensor 204.In this system, a single sensor 204 is used to gather landmark data andto work in combination with the impactor 300A to place an acetabularimplant.

FIGS. 73-75B illustrate various features for clamping structures to theplatform 908. In particular, these figures show fixation pin securementdevices 970 that are incorporated into the platform 908. The fixationpin securement devices 970 can have low profile to be out of the way ofother tools in the surgical field. FIG. 73-73A show one embodiment of apin securement device 970 that includes a compression member 972. Thecannula coupling device 912 can include a similar mechanism to clamp apin disposed through the cannula 924. The platform 908 includes a slotor plurality of slots formed on a surface thereof, e.g., on the topsurface. The slots 974 are larger in at least one direction than thecompression member 972 such that the compression member can fit in theslot and move to some extent therein. The compression member 972 has atapered channel 976. Movement of a tapered member 978 vertically in thetapered channel 976 shifts the compression member 972 to narrow a gap Gbetween the compression member 972 and a rigid feature of the platform.The gap G can be between a curved lateral surface of the compressionmember 972 and a curved surface of the platform 908.

In one method, a pin or other fixation member is advanced through thegap G and into the bone. The platform 908 is positioned on the fixationmember at an appropriate height and the pin securement device 970 isaffixed to the fixation member. The fixation member can be a Steinmannpin or other similar device. In one technique, the tapered member 978 isa threaded elongate body that is advanced along internal threads formedin the platform 908 until the tapered surface thereof acts on thetapered surface 976 to shift the compression member 972 laterally tonarrow the gap G. Further advancement of the tapered member 978 furthershifts the compression member 972 to enhanced securement of the fixationmember. The method can be repeated for a second pin, where one pinextends through the cannula 924 and one extends parallel to the cannula924, but off-set superiorly therefrom on the patient.

FIGS. 74-74B illustrate another approach to a fixation pin securementdevices 970A in which the fixation pin securement device comprises acompression member 972A pivotally mounted to the platform 908. FIG. 74Ashows two compression members 972A, each of which is mounted to pivotabout a pin or shaft 980. The securement device 970A on the left in FIG.74A corresponds to a configuration in which a fixation member can freelypass through a gap G in the mechanism. The securement device 970A on theright in FIG. 74A corresponds to a configuration in which the gap G isnarrowed and a fixation member disposed in the gap G will be securelyclamped and unable to move relative to the platform 908. A rigid surfaceof the platform 908 opposite the pivoting compression member 972 alongwith the compression member holds the fixation member in place.

In one method, pins or other fixation members are placed in the fixationpin securement device 970A and the cannula coupling device 912. In theillustrated embodiment, these devices can employ similar clampingmechanisms. Thereafter, screws 982 are advanced to cause the compressionmember 972 to pivot about the pin or shaft 980 from a first position inwhich the gap G provided between a clamping surface of the compressionmember 972A and a rigid surface of the platform 908 is larger to asecond position in which the gap G is smaller. The second position is aclamped position for the fixation member and will retain the platform inposition until the screw 982 is withdrawn enlarging the gap G.

FIGS. 75-75B illustrate another approach to a fixation pin securementdevices 970B in which the fixation pin securement device comprises acompression member 972B configured to clamp a plurality of segments ofan outside surface of a fixation member. The platform 908 includes aplurality of projections 984 extending upward from an upper surface ofthe platform. The projections preferably are threaded. Each projectionincludes a collet 986 or similar device disposed therein having an innerlumen sized to receive a fixation member. A plurality of slots extendsdownward from an upper surface of the collet 986 and an angled surface988 is disposed between top ends of each member defined between a pairof such slots. A corresponding angled surface 990 is provided on aninside of a cap 992. The cap 992 has internal threads that act on thethreads of the projection 984 to advance the angled surfaces 990 ontothe angled surfaces 988. Further advancement collapses the slots of thecollet 986 causing compression about the outer surface of the fixationmember. FIG. 75 shows that this approach can be used for the fixationpin securement devices 970B and/or for the cannula coupling device 912.

While the systems discussed above are well suited for specificapproaches, the system 900 can be adapted for a posterior approach orfor an anterior approach. This provides a great deal of flexibility tothe surgeon and only adds minimal additional components to a universalkit. The orientation of the axis of rotation A (see FIGS. 70 and 72)enhances the sensitivity of a system that incorporates accelerometersand other sensor drift insensitive components. The home point features968A, 968B enable the surgeon to obtain maximal accuracy by allowing theacquisition of position and orientation data for a number of anatomicallandmarks at close range to the home point position. This allows thesystem to initialize the sensors near the points to be acquired toenhance accuracy.

II. Navigation Using Optical Components

Many of the foregoing systems advantageously use inertial sensors to aidin navigation of procedures. Certain embodiments discussed herein canadvantageously use optical techniques alone or in combination withinertial sensor systems discussed herein to provide additional featuresand advantages.

A. Optical Tracking of System Components

FIG. 65 illustrates one embodiment of a system 800 that includesclose-range optical tracking capabilities. In this context “close range”is a broad term that means near the patient, such as any of in thesurgical field, directly above the pelvis but below the surgeon's head,within the boundaries of the surgical table, etc. This term is intendedto exclude systems where cameras are outside the surgical fields. Closerange greatly reduces or eliminates “line of sight” problems that plaguetraditional optical navigation.

In the illustrated embodiment, a jig system 804 is provided forconnecting to patient bone. The jig system 804 can include any of thefeatures of any of the jig systems discussed herein. For simplicity, thejig system is illustrated with that of FIG. 1, e.g., including thecannula 124 and the platform 136. A surgical orientation device 172A ismounted to the platform 136. The orientation device 172A can be similarto those hereinbefore described, but also includes one or more cameras812. Preferably the orientation device 172A includes two or more cameras812 to enable capture of binocular data. The cameras preferably aresmall cameras, for example the Aptina MT9T111, which is discussed athttp://www.aptina.com/products/soc/m9t111d00stc/. The cones projectingfrom the lower side of the device 172A schematically represent thedirection of the field of view of the cameras 812.

This data can at least be used to determine the heading of and in somecases six degrees of freedom of a stylus 816. The stylus has a distalend 828 configured to touch landmarks as part of a landmark acquisitionmaneuver, as discussed above. A proximal (or other) portion 832 of thestylus 816 has an array of trackers 836 that can be tracked by thecameras 812 to provide orientation, position, heading, attitude, orother combinations of spatial characteristics of portions of the stylus816 or anatomy with which it is coupled.

The cameras 812 can operate without any additional sensor, such asinertial sensors. In some embodiments, the cameras 812 are used inconcert with inertial sensors to confirm or to improve accuracy of thesensors. For example, drift in a rate sensor, e.g., accumulated errors,can be monitored by comparing the output of the rate sensor with theviewed position from the cameras. The system can intervene if the sensoroutput drifts too much, for example, telling the user to reset the ratesensors.

Another optical device such as a laser or an IR emitter 814 can beprovided in the orientation device 172A. An IR emitter can be useful toilluminate the fiduciaries to make them more readily detectable by thecameras under the intense lighting in the surgical field.

B. Optical Component for Femur Tracking

FIGS. 76-78 illustrate an embodiment of a system 600 that includes anoptical component 674. In this context, optical component is a broadterm. The surgical orientation device 172 can comprise optical component674 that can be located on the top side, the bottom side, or sidewallsof the surgical orientation device 172. The optical component 674 cancomprise transparent window integrated into the surgical orientationdevice 172. The windows can permit visible light (e.g. laser light) toemit from the optical component 674 of the surgical orientation device172. The optical component 674 can provide a visual guide to replicatethe original position of the femur relative to the pelvis.

With continued reference to FIG. 76, the optical component 674 cancomprise one or more lasers, which can be configured to project laserlight through the windows described above. For example, the opticalcomponent 674 can comprise a forward laser. The laser light can be usedto project a point, a plane, and or a cross-hair onto a target ortargets, including but not limited to an anatomical feature or landmark.

The optical component 674 can provide alternative or additionalorientation information to a surgeon regarding the orientation of thesurgical orientation device 172. For example, laser light can be used toproject a plane on a portion of bone to indicate a resection line and across-hair laser pattern can be used to ensure alignment along twoperpendicular axes. In certain embodiments, the optical component 674can be used to determine an alignment of an anatomical feature orlandmark. For example, the optical component 674 can project laser lightto a target such as an anatomical feature. The surgeon can mark one ormore points along the line of the projection of the optical component674. The surgeon can complete any steps described herein. The surgeon,thereafter, can verify the one or more points are along the line of theprojection of the optical component 674.

In the illustrated embodiment, the optical component 674 is a componentof the surgical orientation device 172. Other configurations arecontemplated. The optical component 674 can be a component of thefixation base 602. The optical component 674 can be a component of oneor more fixation pins 610, 612. The optical component 674 can be anintegral feature of any component of system 600. The optical component674 can be a separate component from any component of system 600. Theoptical component 674 can be a stand-alone device which attaches to thepelvis.

The system 600 can be modified to accommodate the optical component 674.The fixation base 602C can include a platform 620C as shown in FIGS.79-80. The platform 620C can include a head 609C. The head 609C can becoupled to a platform 611C and a support 613C. The platform 611C and thesupport 613C can function as a clamp with the head 609C. FIG. 80 showsan exploded view of the fixation base 602C.

In the illustrated embodiment, the fixation base 602C can include one ormore fixation devices 615C. In the illustrated embodiment, one fixationdevices 615C is shown but other configurations are contemplated (e.g.,two, three, four, etc.). The fixation device 615C can include one ormore threaded sections. In the illustrate embodiment, the fixationdevice 615C is a screw with a head and a threaded shank. The platform611C can include one or more holes. The support 613C can include one ormore holes. The fixation device 615C can pass through or engage one ormore holes in the support 613C. In some embodiments, each hole in thesupport 613C is threaded. The fixation devices 615C can pass through orengage one or more holes in the platform 611C. In some embodiments, eachhole in the platform 611C is threaded. Rotation of the fixation device615C can causes the support 613C to move toward the platform 611C and/orthe platform 611C to move toward the support 613C. The platform 611C andthe support 613C form a channel 617C. The channel 617C can be sized toaccept the head 609C. When the platform 611C and the support 613C areseparated, the head 608 can have pivotal or polyaxial movement. When theplatform 611C and the support 613C are brought together by the fixationdevice 615C, the head 608C can be fixed in position.

The platform 611C can include the first coupler 632 described herein.The first coupler 632 can couple to the first assembly 604 as describedherein. In FIG. 18, the first coupler 632 can be parallel to the pins610, 612. In FIG. 76, the first coupler 632 can be angled relative tothe pins 610, 612. In the anterior approach, the pins 610, 612 can beoffset from vertical. The probe 678 (not shown) can be bent or curved asdescribed herein. The shape of the probe 678 can facilitate the touchingof points or anatomical landmarks in the anterior approach.

The assembly shown in FIG. 76 can permit the surgical orientation deviceto be moved relative to the anatomy of the patient. The clamping of theplatform 611C and the support 613C can fix the position of the surgicalorientation device 172 during surgery. The display of the surgicalorientation device 172 can indicate whether the optical component 674 ison or off. The display of the surgical orientation device 172 caninclude an instructions related to the method of using the opticalcomponent 674.

In a preferred arrangement, the surgical orientation device 172 can bepositioned and/or moved until the optical component 674 projects a beamon a portion of the anatomy. To achieve this centering, the opticalcomponent 674 can emit a laser beam or beams distally from the surgicalorientation device 172. This laser beam or beams can illuminate aportion of the femur. This laser beam or beams can illuminate a portionof the knee joint. This laser beam or beams can illuminate a portion ofthe tibia. This laser beam or beams can illuminate a portion of theankle. This laser beam or beams can illuminate a portion of the foot.This laser beam or beams can illuminate a portion of the footconstrained within a positioning boot. The surgical orientation device172 can be moved until the laser beam is aligned with at least oneanatomical region. In some methods, the laser beam is aligned with atleast one anatomical region with little soft tissue. The soft tissue maymove relative to the underlying bone. The surgeon can select locationsto mark where the skin is close to the underlying bone.

The optical component 674 can be used in conjunction with the anteriorand posterior approach described herein. When measuring changes in leglength and lateral joint offset, the apparent changes are sensitive tochanges in the orientation of the femur relative to the pelvis. Thechanges are particularly sensitive to the abduction angle. The changesare moderately sensitive to the rotation about the mechanical axis ofthe femur. There may be two methods available to the surgeon. The firstmethod is to reposition the femur prior to measuring the change suchthat the orientation of the femur relative to the pelvis is the same asthat when the preoperative baseline measurement was made. Surgeonsattempt to use the first method but this method is not very accurate.The method is not accurate primarily because the surgeon has poorvisibility of the pelvis of the patient, which is hidden by soft tissueand surgical drapes.

The second method is to measure the orientation of the femur relative topelvis during preoperative baseline and postoperatively and then correctfor changes in orientation by doing a virtual rotation about thepostoperative center of rotation of the femur. The second method isdescribed herein with respect to the posterior approach and the anteriorapproach. The second method may require obtaining three points of thefemur, such as points 690 shown in FIGS. 24A and 25C. The second methodmay require calculating the center of rotation (COR) of the hip usingthe set of points on the rim of the shell, as shown in FIG. 33. Thesecond method is usually used in navigation systems but adds extrasteps. In the case of the posterior approach described above, forexample, three points 690 on the femur, femur tracker 686, 686A or femurbase 687A must be registered to resolve for the femur orientationpreoperatively and then postoperatively each time the leg length is tobe measured. Also, the center of rotation must be determined which isdone by registering three points on the acetabular cup after it has beeninserted.

The optical component 674 can reduce the number of registrations. Theoptical component 674 can be mounted on the pelvis. The orientation ofthe optical component 674 can be fixed throughout the procedure. Theoptical component 674 can project a beam distally onto the leg. Thesurgeon can mark one or more points. These marks can guide the surgeonin replicating the orientation of the femur relative to the pelvis eachtime a leg length measurement is needed.

In some embodiments, the optical component 674 can be a “fan” stylelaser projection. The optical component 674 can project a line orpattern onto the leg. The method can, in variation, include any of thefollowing steps. The following method is described in the context of ananterior approach in which the patient is supine as shown in FIG. 76.The method can include positioning the operative leg in a fully extendedposition to simulate a standing position. The method can includeprojecting the laser onto the anterior surface of the leg, running upthe foot. The laser could be mounted on a lockable ball joint tofacilitate adjustments to line up the laser and then lock it in place,as shown in FIG. 79. The method can include marking one or more marks Lmon the surface of the leg and foot coincident with the laser line. Themethod can include performing the baseline leg length measurement orregistration on the exposed bone of the femur as close to the center ofrotation as possible. This may minimize errors. This step can includeplacing a mark Fm on skin over the femur as described herein. Forexample, a mark placed at the distal femur may provide enhanced accuracyby eliminating error due to movement of the joints distal thereof. Sucha location may also simplify an accurate procedure by eliminating theneed to constrain the distal joints including the knee and ankle. Themethod can include performing the hip replacement. The method caninclude replicating the orientation of the femur by lining up the one ormore marks Lm with the laser line again. The method can includeperforming the postoperative leg length measurement to determine changesin leg length and lateral offset. This step can include registering themark Fm on the femur as described herein.

The method described herein can reduce the need to add a femur tracker686, 686A or femur base 687A to the femur. The method described hereincan reduce the need to drill holes in the femur to attach the femurtracker 686, 686A or femur base 687A. This can prevent fractures orfurther damage to the femur. In some methods, the optical component 674is used in combination with a camera. The camera can be the camera 684described herein. The camera can be camera 812 described herein. Thecamera can capture a photographic image of the laser or laser beam. Thecamera can capture a photographic image of the one or more marks Lm. Thecamera can capture a photographical image of the leg and/or foot. Thesurgical orientation device 172 and/or the orientation sensing device204 as described herein can convert the photographic image toorientation and/or positional information of the anatomy of the patient.

Although these inventions have been disclosed in the context of certainpreferred embodiments and examples, it will be understood by thoseskilled in the art that this application extends beyond the specificallydisclosed embodiments to other alternative embodiments and/or uses ofthe invention and obvious modifications and equivalents thereof. Inaddition, while a number of variations of the inventions have been shownand described in detail, other modifications, which are within the scopeof the inventions, will be readily apparent to those of skill in the artbased upon this disclosure. It is also contemplated that variouscombinations or sub-combinations of the specific features and aspects ofthe embodiments may be made and still fall within the scope of theapplication. For example, the application contemplates the connectionhub alone or in combination with any of the other modules could comprisea separate aspect. Or, any one or a combination of the modules could bedirectly connected to an umbrella hub or overhead support to formanother separate aspect. Accordingly, it should be understood thatvarious features and aspects of the disclosed embodiments can becombined with or substituted for one another in order to form varyingmodes of the disclosed embodiments. Thus, it is intended that the scopeof the present invention herein disclosed should not be limited by theparticular disclosed embodiments described above, but should bedetermined only by a fair reading of the claims that follow.

Similarly, this method of disclosure, is not to be interpreted asreflecting an intention that any claim require more features than areexpressly recited in that claim. Rather, as the following claimsreflect, inventive aspects lie in a combination of fewer than allfeatures of any single foregoing disclosed embodiment. Thus, the claimsfollowing the Detailed Description are hereby expressly incorporatedinto this Detailed Description, with each claim standing on its own as aseparate embodiment.

1-64. (canceled)
 65. A method of performing a hip joint replacementprocedure, the hip joint comprises a pelvis and a femur that is movablerelative to the pelvis, the method comprising: registering the femurprior to positioning an acetabular shell in the hip joint comprising:registering a rotational position of the femur about a mechanical axisof the femur; positioning a tip of the probe in contact with a point onthe femur or a fixation structure coupled to the femur; positioning anacetabular shell in the hip joint; and determining an aspect of therelative position and/or orientation of the femur after positioning theacetabular shell in the hip joint comprising: moving the femur to therotational position of the femur after positioning the acetabular shell;and positioning the tip of the probe in contact with the point on thefemur or the fixation structure coupled to the femur.
 66. The method ofclaim 65, further comprising coupling the fixation structure to thefemur, wherein the point comprises a divot.
 67. The method of claim 65,wherein registering the rotational position of the femur comprisesprojecting light onto a target.
 68. The method of claim 65, whereinregistering the rotational position of the femur comprises marking atarget along a pattern of light.
 69. The method of claim 68, whereinmoving the femur to the rotational position of the femur comprisesaligning the marking with the pattern of light.
 70. The method of claim65, wherein moving the femur to the rotational position of the femurcomprises projecting light onto a target.
 71. The method of claim 65,further comprising positioning the patient in a supine position.
 72. Themethod of claim 65, further comprising mounting a laser projectingdevice to the pelvis, wherein registering the rotational position of thefemur and moving the femur to the rotational position of the femurutilize the laser projecting device.
 73. The method of claim 65, furthercomprising displaying a change in leg length.
 74. The method of claim65, further comprising displaying a change in joint offset.
 75. A methodof performing a hip joint replacement procedure, the hip joint comprisesa pelvis and a femur that is movable relative to the pelvis, the methodcomprising: registering an orientation of a probe when a tip of theprobe contacts a point on the femur or a fixation structure coupled tothe femur; registering rotation of the femur about a mechanical axis ofthe femur; positioning an acetabular shell in the hip joint; moving thefemur to the registered rotation of the femur about the mechanical axisof the femur; and positioning the tip of the probe in contact with thepoint on the femur or the fixation structure to determine an aspect ofthe relative position and/or orientation of the femur after positioningthe acetabular shell.
 76. The method of claim 75, wherein registeringrotation of the femur about the mechanical axis of the femur comprisesprojecting light onto a target and marking the incidence of light. 77.The method of claim 76, wherein moving the femur to the registeredrotation of the femur comprises projecting light onto the target andaligning the marking with the incidence of light.
 78. The method ofclaim 75, further comprising displaying a change in leg length and/orjoint offset.
 79. A method of performing a hip joint replacementprocedure, the hip joint comprises a pelvis and a femur that is movablerelative to the pelvis, the method comprising: registering anorientation of a probe when a tip of the probe contacts a point on thefemur or a fixation structure coupled to the femur, wherein the femurcomprises an initial rotation about a mechanical axis of the femur;positioning an acetabular shell in the hip joint; replicating theinitial rotation of the femur about the mechanical axis of the femur;and positioning the tip of the probe in contact with the point on thefemur or the fixation structure to determine an aspect of the relativeposition and/or orientation of the femur after positioning theacetabular shell.
 80. The method of claim 79, wherein replicating theinitial rotation of the femur about the mechanical axis of the femurcomprises projecting a pattern of light onto a target.
 81. The method ofclaim 79, wherein replicating the initial rotation of the femur aboutthe mechanical axis of the femur comprises aligning a marking on atarget with light projecting from a light projecting device.
 82. Themethod of claim 79, wherein a change in leg length and/or joint offsetis determined based on positioning the tip of the probe in contact withthe point on the femur or the fixation structure.
 83. The method ofclaim 79, wherein at least one of a change in leg length and a change injoint offset is displayed.
 84. The method of claim 79, furthercomprising coupling the fixation structure to the femur, wherein thepoint comprises a divot.